ISLAMABAD, Pakistan (AP) -- Pakistan warned U.S. troops not to intrude on its territory Friday, after the two anti-terror allies traded fire along the volatile border with Afghanistan.
Thursday's five-minute clash adds to already heightened tensions at a time the United States is stepping up cross-border operations in a region known as a haven for Taliban and al-Qaida militants.
The clash - the first serious exchange with Pakistani forces acknowledged by the U.S. - follows a string of other alleged border incidents and incursions that have angered many here.
Speaking in New York, Pakistan's president tried to downplay the incident, saying only "flares" were fired at foreign helicopters that he said strayed into his country from Afghanistan.
U.S. and NATO military officials said the ground troops and helicopters were in Afghan territory.
Meanwhile, a bomb blast caused a train to derail in eastern Punjab province, killing four people and wounding 15 others, authorities said. The prime minister said he had ordered an investigation into the blast.
The escalating violence in Pakistan was also felt as far south as Karachi.
Police raided a militant hideout Friday in Pakistan's largest city, triggering a shootout during which three suicide bombers blew themselves up. The body of a man held in handcuffs was found in the rubble, police said.
The three men were suspected of planning an attack on a "high-profile" target in Karachi, said Sindh police chief Babar Khattak, giving no more details. The police raided the house in Karachi on a tip from a leader of an al-Qaida-linked militant group, Khattak said.
"Police definitely averted a big attack from happening in this city," he said.
Police seized at least 22 pounds of explosives, two suicide jackets, seven pistols and 12 hand grenades from the Karachi house, which was badly damaged by the explosions.
The prisoner whose body was discovered in the rubble was identified as a wealthy supplier of fuel and goods to U.S. and NATO forces in Afghanistan, senior police official Aleem Jaffry told The Associated Press.
Pakistani government spokesman Akram Shaheedi urged U.S.-led coalition forces "not to violate territorial sovereignty of Pakistan as it is counterproductive to the war on terror."
"It has been Pakistan's policy that we will not allow anyone to violate our sovereignty, and we will continue to defend our territorial sovereignty," he said Friday.
The clash occurred as new Pakistani President Asif Ali Zardari was in New York meeting with U.S. Secretary of State Condoleezza Rice, and Afghan President Hamid Karzai was scheduled to meet with U.S. President George W. Bush on Friday.
Two American OH-58 reconnaissance helicopters, known as Kiowas, were on a routine patrol in the eastern province of Khost when they received small arms fire from the Pakistani border post, said Tech Sgt. Kevin Wallace, a U.S. military spokesman in Bagram. There was no damage to aircraft or crew, officials said.
Sarwar Shah, a 45-year-old bus driver who witnessed the incident, said two foreign choppers and a military vehicle were involved.
"I heard gunshots, but it lasted only for six or seven minutes," he told The Associated Press.
He said he was happy to see the Pakistan army firing at the helicopters, "If the army needs our help, we will help it against the Americans," Shah said.
U.S. Central Command spokesman Rear Adm. Greg Smith said the helicopters had been escorting U.S. troops and Afghan border police. When the helicopters were fired on, the ground forces fired rounds meant not to hit the Pakistani troops, but "to make certain that they realized they should stop shooting," Smith said from Centcom headquarters in Florida.
The Pakistani forces fired back during a skirmish that lasted about five minutes. The joint patrol was moving about a mile inside Afghanistan, with the helicopters above, Smith said.
The Pakistani military disputed the U.S. version, saying its troops fired warning shots when the two helicopters crossed over the border - and that the U.S. helicopters fired back.
"When the helicopters passed over our border post and were well within Pakistani territory, own security forces fires anticipatory warning shots. On this, the helicopters returned fire and flew back," a Pakistani military statement said.
In New York, Zardari said his military fired only "flares" at foreign helicopters that he claimed had strayed across the border from Afghanistan.
Zardari said before his meeting with Rice that his forces fired only as a way "to make sure that they know that they crossed the border line."
Later, in a speech at the U.N. General Assembly, Zardari vowed to continue the fight against terrorists but warned against allied incursions into Pakistan.
"Just as we will not let Pakistan's territory to be used by terrorists for attacks against our people and our neighbors, we cannot allow our territory and our sovereignty to be violated by our friends," Zardari said.
"Unilateral actions of great powers should not inflame the passions of allies," he said.
The Pakistani military said the matter was "being resolved" in consultations between the army and the NATO force in Afghanistan. A NATO statement said the militaries were "working together to resolve the matter."
The shooting comes amid a string of cross-border incidents, including a highly unusual raid by American commandos into Pakistan's tribal areas on Sept. 3 that left at least 15 people reportedly dead, and the apparent crash landing because of possible mechanical failure of a U.S. spy drone this week in Pakistan's tribal areas.
Maj. Gen. Athar Abbas, a Pakistani army spokesman, said last week that Pakistani field commanders have previously tolerated international forces crossing a short way into the country because of the ill-defined and contested nature of the mountainous frontier.
"But after the (Sept. 3) incident, the orders are clear," Abbas said. "In case it happens again in this form, that there is a very significant detection, which is very definite, no ambiguity, across the border, on ground or in the air: open fire."
Talat Masood, a military and political analyst, warned the cross-border raids were undermining support for American in Pakistani and risked destabilizing the country, where the new government was still asserting its authority.
"These incursions strengthen the hands of the militants, that is the result of this," Masood said. "You don't want to strengthen them, you want to weaken them."
Associated Press writers Steve Graham in Islamabad, Pauline Jelinek in Washington and Matthew Lee in New York contributed to this report.
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