At least 24 people have been killed in a series of bomb explosions in India's north-eastern state of Assam, police say.

More than 60 others were injured in at least nine blasts, the majority of them in the state capital, Guwahati.

No one has claimed responsibility for the blasts, but police suspect the separatist United Liberation Front of Assam (Ulfa).

Security forces have been fighting separatist rebels in Assam for decades.

The explosions in Guwahati and the towns of Kokrajhar, Barpeta Road and Bongaigaon occurred within an hour after 1100 local time (0530 GMT).

Six people were killed in the first explosion in front of the deputy commissioner's office in Guwahati.

Five others were killed in the second explosion at Ganeshguri near the state secretariat and four in Panbazar in central Guwahati.

"The impact of the blast was so huge, a packed bus got half burnt and we pulled out lot of injured people and sent them to hospital," Pankaj Goswami, an eyewitness in Guwahati, told Reuters news agency.

Angry crowds attacked the police with stones after the blasts in the city. Dozens of people were injured in the clashes, Reuters reports.

Five others were killed in three explosions that rocked the western town of Kokrajhar.

Explosions were also reported in the towns of Barpeta Road and Bongaigaon, two towns in western Assam.

Assam police chief RN Mathur said most of the bombs were "planted in cars".

'Massive strikes'

Intelligence officials said the separatist United Liberation Front of Assam (Ulfa) was responsible for the blasts.

Most fighters in one of Ulfa's elite strike battalions have announced a ceasefire with the government and the security forces have attacked and killed many other Ulfa fighters in recent weeks.

"So the Ulfa is striking back in a massive way by taking on soft targets," Assam police chief R N Mathur said.

"No other group can trigger so many blasts in so many places in such a coordinated fashion."

The group began an armed rebellion against what it describes as colonial rule by Delhi in 1979. Thousands of people have died in the violence.

An effort to start peace talks between the rebels and the Indian government broke down in 2006.

The rebels are seeking a separate homeland for the Assamese people and demanding the departure of the non-indigenous population, particularly Hindi speakers.

India has been rocked by a number of explosions in the past few months, and many of them have been blamed on suspected local Islamic groups.

But local separatists have been held responsible for recent explosions in north-eastern cities.

Two north-eastern state capitals - Agartala, capital of Tripura, and Imphal, capital of Manipur - have been rocked by serial explosions this month.

At least 20 people were killed and more than 100 injured in the explosions.