Pakistani troops and tribesmen opened fire on two U.S. helicopters that crossed into the country from neighboring Afghanistan, intelligence officials said Monday.
The helicopters did not return fire and re-entered Afghan airspace without landing, the officials said.
Pakistan's army and the U.S. military in Afghanistan said they had no information on the reported incursion late Sunday, 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 said to have killed 15 people have angered and embarrassed Pakistani leaders while signaling Washington's impatience with Pakistani efforts to clear out militant havens.
During a recent speech to Parliament, newly elected President Asif Ali Zardari, who is considered U.S.-friendly, warned that no country would be allowed to violate Pakistan's sovereignty in the name of the war on terror.
Zardari is on his way to New York to attend the U.N. General Assembly, and he is expected to meet President Bush.
The two intelligence officials spoke on condition of anonymity because they were not authorized to speak to media.
They said informants in the field told them of the incursion around one mile inside the disputed and poorly demarcated border in the Alwara Mandi area in North Waziristan, a tribal region the U.S. considers a sanctuary for Taliban and al-Qaida fighters.
A week ago, U.S. helicopters reportedly landed near Angoor Ada, a border village in nearby South Waziristan, but returned toward Afghanistan after troops fired warning shots.
A Pakistani military spokesman said last week that troops had orders to open fire in case of another cross-border raid by foreign troops.
