In this image taken by Closed Circuit TV footage and released by Interior ministry via APTN, guards look at a burning large dump truck, right, after the initial small explosion at the gate of Marriott Hotel in Islamabad, Pakistan, Saturday, Sept. 20, 2008. Rescuers pulled more bodies from the shell of the truck-bombed Marriott Hotel in Pakistan’s capital Sunday, pushing the death toll from one of the country’s worst-ever terrorist strikes to 53, including the Czech ambassador and a second American. (AP)

ISLAMABAD, Pakistan (AP) - Pakistani troops and tribesmen opened fire when two U.S. helicopters crossed into the country from neighboring Afghanistan, intelligence officials said Monday.

The alleged incident late Sunday in North Waziristan came as the Muslim country struggled to respond to a suicide bombing at a luxury hotel in the capital that killed at least 53.

Pakistan’s army and the U.S. military in Afghanistan said they had no information on the reported incursion, which will likely add to tensions between Islamabad and Washington.

A spate of suspected U.S. missile strikes into Pakistan’s border region and a raid by U.S. commandos that killed about 15 people have angered and embarrassed Pakistani leaders.

President Asif Ali Zardari is in New York to attend the U.N. General Assembly. The newly elected leader is also expected to meet U.S. President George W. Bush.

The two intelligence officials spoke on condition of anonymity because they were not authorized to speak to the media. They said informants in the field told them of the incursion about one mile (two kilometers) inside the disputed and poorly demarcated border in the Alwara Mandi area.

The helicopters did not return fire and re-entered Afghan airspace without landing, the officials said.

A week ago, U.S. helicopters reportedly landed near Angoor Ada, a border village in South Waziristan, but returned toward Afghanistan after troops fired warning shots.

A military spokesman said last week that Pakistani soldiers had orders to open fire in case of another cross-border raid by U.S. troops.

Meanwhile, suspicion hardened that al-Qaida or the Taliban were behind Saturday’s blast at the Marriott hotel in Islamabad. Some 270 people were wounded, while the dead included the Czech ambassador and two U.S. Department of Defense employees.