Many of the roads out of Tashkent have been closed

American Secretary of State Colin Powell made the offer in a telephone call to his Uzbek counterpart.

Uzbekistan says 23 people died when suspected militants blew themselves up during a gun battle with special forces in the capital, Tashkent, on Tuesday.

On Sunday and Monday, 19 people were killed and 26 injured in bombs in Tashkent and the city of Bukhara.

Co-operation

The US and Uzbekistan have been close allies since the 11 September attacks, after which the Uzbek government made its airspace and military facilities available to US forces, facilitating the operation to remove the Taleban in neighbouring Afghanistan.

Uzbekistan has since become an important strategic outpost for the US.

More democracy is the best antidote to terror Richard Boucher US State Department spokesman Analysis: Causes of unrest

State Department spokesman Richard Boucher said that while the two countries may have co-operated in the war on terrorism, Uzbekistan must introduce democratic reforms: "More democracy is the best antidote to terror," he said.

No-one has claimed responsibility for the attacks, the bloodiest seen in the former Soviet republic for years. Uzbek officials have suggested one group, Hizb ut-Tahrir, could be to blame.

But the group, which has its headquarters in London, has denied any involvement, saying it "does not engage in terrorism, violence or armed struggle".

Another group under suspicion is the home-grown Islamic Movement of Uzbekistan (IMU).

The group's leader Tahir Yuldashev is accused of orchestrating the series of deadly bomb attacks in Tashkent in 1999.

However, Shahida Tulaganova of the BBC's Central Asia Service says that the group, which fought alongside the Taleban during the Afghan conflict is now in tatters, with many of its leaders being held by the US in Guantanamo Bay, Cuba.

Security crackdown

Twenty three people, 20 suspected militants and three police officers, died in Tuesday's shoot out, which lasted more than five hours.

The militants took refuge in a house on the Yagandach housing estate in the north of the city, which was quickly surrounded by police.

The siege only ended when the insurgents blew themselves up.

In an effort to curb the violence President Islam Karimov has temporarily sealed the country's borders and ordered huge numbers of police onto the streets to curb the violence.

But the BBC's Monica Whitlock, in Tashkent, says this measure may have increased the violence.

All the attacks seem to be directed at police targets and now there are lone officers dotted around Tashkent's streets, highly visible and vulnerable to attack, she says.

Our correspondent says the police are widely seen as the main instrument of government in Uzbekistan, and are very much disliked and feared in some circles.