ISRAELI commandos from the elite Sayeret Matkal unit – almost certainly dressed in Syrian uniforms – made their way stealthily towards a secret military compound near Dayr az-Zawr in northern Syria. They were looking for proof that Syria and North Korea were collaborating on a nuclear programme.

Israel had been surveying the site for months, according to Washington and Israeli sources. President George W Bush was told during the summer that Israeli intelligence suggested North Korean personnel and nuclear-related material were at the Syrian site.

Israel was determined not to take any chances with its neighbour. Following the example set by its raid on an Iraqi nuclear reactor at Osirak 1981, it drew up plans to bomb the Syrian compound.

But Washington was not satisfied. It demanded clear evidence of nuclear-related activities before giving the operation its blessing. The task of the commandos was to provide it.

News of the secret ground raid is the latest piece of the jigsaw to emerge about the mysterious Israeli airstrike. Israel has imposed a news blackout, but has not disguised its satisfaction with the mission. The incident also reveals the extent of the cooperation between America and Israel over nuclear-related security issues in the Middle East. The attack on what Israeli defence sources now call the “North Korean project” appears to be part of a wider, secret war against the nonconventional weapons ambitions of Syria and North Korea which, along with Iran, appears to have been forging a new “axis of evil”.

The operation was personally directed by Ehud Barak, the Israeli defence minister, who is said to have been largely preoccupied with it since taking up his post on June 18.

It was the ideal mission for Barak, Israel’s most decorated soldier and legendary former commander of the Sayeret Matkal, which shares the motto “Who Dares Wins” with Britain’s SAS and specialises in intelligence-gathering deep behind enemy lines.

President Bush refused to comment on the air attack last week, but warned North Korea that “the exportation of information and/or materials” could jeopard-ise plans to give North Korea food aid, fuel and diplomatic recognition in exchange for ending its nuclear programmes.

Diplomats in North Korea and China said they believed a number of North Koreans were killed in the raid, noting that ballistic missile technicians and military scientists had been working for some time with the Syrians.

A senior Syrian official, Sayeed Elias Daoud, director of the Syrian Arab Ba’ath party, flew to North Korea via Beijing last Thursday, reinforcing the belief among foreign diplomats that the two nations are coordinating their response to the Israeli strike.

The growing assumption that North Korea suffered direct casualties in the raid appears to be based largely on the regime’s unusually strident propaganda on an issue far from home. But there were also indications of conversations between Chinese and North Korean officials and intelligence reports reaching Asian governments that supported the same conclusion, diplomats said.

Jane’s Defence Weekly reported last week that dozens of Iranian engineers and Syrians were killed in July attempting to load a chemical warhead containing mustard gas onto a Scud missile. The Scuds and warheads are of North Korean design and possibly manufacture, and there are recent reports that North Koreans were helping the Syrians to attach airburst chemical weapons to warheads.

Yesterday, while Israelis were observing Yom Kippur, the holiest day in the Jewish calendar, the military was on high alert after Syria promised to retaliate for the September 6 raid. An Israeli intelligence expert said: “Syria has retaliated in the past for much smaller humiliations, but they will choose the place, the time and the target.”

Critics of Bashar al-Assad, the Syrian president, believe he has shown poor judgment since succeeding his father Hafez, Syria’s long-time dictator, in 2000. According to David Schenker, of the Washington Institute for Near East Policy, he has provoked the enmity of almost all Syria’s neighbours and turned his country into a “client” of Iran.

Barak’s return to government after making a fortune in private business was critical to the Israeli operation. Military experts believe it could not have taken place under Amir Peretz, the defence minister who was forced from the post after last year’s ill-fated war in Lebanon. “Barak gave Olmert the confidence needed for such a dangerous operation,” said one insider.

The unusual silence about the airstrikes amazed Israelis, who are used to talkative politicians. But it did not surprise the defence community. “Most Israeli special operations remain unknown,” said a defence source.

When Menachem Begin, then Israeli prime minister, broke the news of the 1981 Osirak raid, he was accused of trying to help his Likud party’s prospects in forthcoming elections.

Benjamin Netanyahu, who leads Likud today, faced similar criticism last week when he ignored the news blackout, revealed that he had backed the decision to strike and said he had congratulated Olmert. “I was a partner from the start,” he claimed.

But details of the raid are still tantalisingly incomplete. Some analysts in America are perplexed by photographs of a fuel tank said to have been dropped from an Israeli jet on its return journey over Turkey. It appears to be relatively undamaged. Could it have been planted to sow confusion about the route taken by the Israeli F-15I pilots?

More importantly, questions remain about the precise nature of the material seized and about Syria’s intentions. Was Syria hiding North Korean nuclear equipment while Pyongyang prepared for six-party talks aimed at securing an end to its nuclear weapons programme in return for security guarantees and aid? Did Syria want to arm its own Scuds with a nuclear device?

Or could the material have been destined for Iran as John Bolton, the former US ambassador to the United Nations, has suggested? And just how deep is Syrian and North Korean nuclear cooperation anyway?

China abruptly postponed a session of the nuclear disarmament talks last week because it feared America might confront the North Koreans over their weapons deals with Syria, according to sources close to the Chinese foreign ministry. Negotiations have been rescheduled for this Thursday in Beijing after assurances were given that all sides wished them to be “constructive”.

Christopher Hill, the US State Department negotiator, is said to have persuaded the White House that the talks offered a realistic chance to accomplish a peace treaty formally ending the 1950-1953 Korean war, in which more than 50,000 Americans died. A peace deal of that magnitude would be a coup for Bush – but only if the North Koreans genuinely abandon their nuclear programmes.

The outlines of a long-term arms relationship between the North Koreans and the Syrians are now being reexamined by intelligence experts in several capitals. Diplomats in Pyongyang have said they believe reports that about a dozen Syrian technicians were killed in a massive explosion and railway crash in North Korea on April 22, 2004.

Teams of military personnel wearing protective suits were seen removing debris from the section of the train in which the Syrians were travelling, according to a report quoting military sources that appeared in a Japanese newspaper. Their bodies were flown home by a Syrian military cargo plane that was spotted shortly after the explosion at Pyongyang airport.

In December last year, the Kuwaiti newspaper Al Seyassah quoted European intelligence sources in Brussels as saying that Syria was engaged in an advanced nuclear programme in its northeastern province.

Most diplomats and experts dismiss the idea that Syria could master the technical and industrial knowhow to make its own nuclear devices. The vital question is whether North Korea could have transferred some of its estimated 55 kilos of weapons-grade plutonium to Syria. Six to eight kilos are enough for one rudimentary bomb.

“If it is proved that Kim Jong-il sold fissile material to Syria in breach of every red line the Americans have drawn for him, what does that mean?” asked one official. The results of tests on whatever the Israelis may have seized from the Syrian site could therefore be of enormous significance.

The Israeli army has so far declined to comment on the attack. However, several days afterwards, at a gathering marking the Jewish new year, the commander-in-chief of the Israeli military shook hands with and congratulated his generals. The scene was broadcast on Israeli television. After the fiasco in Lebanon last year, it was regarded as a sign that “we’re back in business, guys”.