The United States says Pakistan is serving as a "platform for terrorism" and that this must stop.

The US ambassador to Islamabad, Nancy Powell, also urged Pakistan to ensure that militant groups are no longer able to cross into Indian-administered Kashmir.

Correspondents say Ms Powell's comments are unusually strong for a serving US ambassador in Pakistan and amount to a rebuke to the government there.

Ms Powell was speaking in the city of Karachi where, exactly one year ago, US journalist Daniel Pearl was kidnapped by Islamic militants who later killed him.

He was investigating links between Pakistani militant groups and Osama bin Laden's al-Qaeda movement.

Cease-fire call

"The government of Pakistan must ensure its pledges are implemented to prevent infiltration across the Line of Control (LoC) and end the use of Pakistan as a platform for terrorism," Ms Powell told a meeting of US businessmen in Karachi.

Kashmir poses a serious threat to regional stability

India has long maintained that Pakistan has allowed militants to cross the LoC which divides Kashmir into Indian and Pakistani- administered areas.

Tens of thousands of people have died in violence in Indian-administered Kashmir, which has been the focus of two wars between India and Pakistan.

Ms Powell called for the fighting to stop.

"We continue to look for ways to encourage peace in Kashmir.

"One important step could be a cease-fire along the Line of Control."

A BBC correspondent in Islamabad says it is the first time a US ambassador to Islamabad has made such strong comments.

Comments 'will hurt'

Last year, Pakistan President Pervez Musharraf promised to halt militant attacks across the LoC.

He had some success until about six months ago when American and Indian agencies said there was a pronounced increase in attacks.

These reached a peak in the lead-up to the elections in Indian-administered Kashmir late last year.

Our correspondent says the American rebuke will hurt Pakistan, coming as its foreign minister, Khurshid Kasuri, is in the United States preparing for a meeting with Secretary of State Colin Powell.

Colin Powell and Khurshid Kasuri will try to ease ties

The pair will try to ease difficulties that have recently strained relations.

One was the difference of opinion over whether US forces in Afghanistan could cross the border into Pakistan to pursue al-Qaeda suspects.

The issue arose after US forces bombed a disused school on the Pakistan-Afghan border this month after a Pakistani border guard fired on a US patrol.

Another problem has been the new US immigration policy that requires nationals from Pakistan and 19 other nations to register with authorities.

Pakistan is upset its nationals have been included as it sees itself as a front-line state in the war on terror.

India, however, says it encourages terror by supporting militants attacking civilians and security forces in Kashmir.