KABUL: Afghan President Hamid Karzai on Sunday ratcheted up his criticism of Washington during a visit of the U.S. defense secretary, underscoring tension between allies struggling to stabilise the country ahead of a NATO troop withdrawal.

Karzai accused the United States and the Taliban of colluding to convince Afghans that foreign forces were needed to maintain peace in the country beyond next year, when most foreign combat forces are due to leave.

Then, his government alleged U.S.-led forces and Afghans working with them were abusing and arresting university students and urged them to stop.Referring to two bomb attacks on Saturday that killed 17 people, Karzai said the blasts were aimed at convincing people that the Taliban would return if U.S. forces withdrew.

"Those bombs ... were in the service of the Americans to keep foreigners in Afghanistan longer, to keep them here," Karzai told a gathering to mark International Women's Day.

The Taliban have for years demand the withdrawal of foreign forces and have never suggested that they wanted them to stay.

Karzai has a history of making inflammatory remarks, particularly railing against the United States with which he has an uneasy relationship.

The issue of U.S. troop levels after most U.S.-led NATO combat troops withdraw by the end of 2014 will be one of the main subjects on the agenda at talks between Karzai and U.S. Defense Secretary Chuck Hagel, who is in Afghanistan to visit U.S. troops.

A joint news conference that had been scheduled for them was cancelled because of security worries, a U.S. official said.

Karzai also said the Taliban and the United States had been holding talks in the Gulf Arab state of Qatar on a "daily basis", but the militant group and Washington denied they had resumed efforts on dialogue that stalled a year ago.

The U.S. government has said it remained committed to political reconciliation involving talks with the Taliban but progress would require agreement between the Afghan government and the insurgents.

"This is simply incorrect," said a U.S. official, who declined to be identified, when asked about Karzai's remarks about the talks.

DEADLINE

The Taliban spokesman in Afghanistan, Zabihullah Mujahid, also denied that negotiations with the United States had resumed and said no progress had been made since they were suspended.

"The Taliban strongly rejects Karzai's comments," he said.

The Kabul government has been pushing hard to get the Taliban to the negotiating table before foreign troops withdraw.

Afghan officials have not held direct talks with the militants, who were toppled in 2001 and have proven resilient after more than a decade of war with Western forces.

U.S. diplomats have been seeking to broaden exploratory talks with the Taliban that began clandestinely in Germany in late 2010 after the Taliban offered to open a representative office in Qatar.

Regional power Pakistan indicated a few months ago that it would support the peace process by releasing Afghan Taliban detainees who may help promote the peace process. But there have been no tangible signs the move advanced reconciliation.

Hagel arrived on Friday for his first trip abroad as defense secretary.

His visit coincides with the passing of a deadline imposed by Karzai for U.S. special forces to leave the province of Wardak, after Karzai accused them of overseeing torture and killings in the area.

U.S. forces have denied involvement in any abuses and it was not clear if they were leaving Wardak by the deadline.

The Afghan government said in a statement the abuse and detention of university students was a violation of sovereignty and it called on U.S.-led forces to stop it.

The government said in a decree security forces and university authorities had to stop foreign forces going in to universities.