The US ambassador at the UN, Zalmay Khalilzad, has accused Saudi Arabia of undermining efforts to stabilise Iraq.
Mr Khalilzad said he was referring to Saudi Arabia in an article last week in which he said US friends were pursuing destabilising policies.
His comments came just hours before a Middle East tour by the Secretary of State, Condoleezza Rice, and the Defence Secretary, Robert Gates.
The two top officials will visit Saudi Arabia and Egypt together.
Ms Rice and Mr Gates are expected to ask Saudi King Abdullah for greater cooperation on Iraq.
Mr Khalilzad told CNN in an interview that his opinion piece for the New York Times last week was referring to Saudi Arabia among other countries.
"We would expect and want them to help us on this strategic issue more than they are doing. And at times, some of them are not only not helping, [they] are doing things that undermine the effort to make progress," he said.
His comments follow newspaper reports, quoting senior US defence officials, on the planned sale of arms worth $20bn (£9.8bn) to Saudi Arabia and other Gulf states over the next decade.
To counter objections by Israel and its supporters in Congress, the officials said the Jewish state would be offered significantly increased military aid.
But the arms sale is still set to encounter opposition in Washington.
Two Democratic congressmen, Anthony Weiner and Jerrold Nadler of New York, said on Sunday they would introduce legislation to block the deal.
"Saudi Arabia should not get an ounce of military support from the US until they unequivocally denounce terrorism and take tangible steps to prevent it," Mr Weiner said at a news conference.
The congressmen pointed out that 15 out of 19 hijackers who carried out the 11 September 2001 attacks were Saudi nationals.
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