ISLAMABAD (Reuters) - Pakistani security officials said on Monday that troops had fired on U.S. military helicopters and forced them to turn back to Afghanistan, but both the Pakistani and American militaries denied the incident.

A U.S. helicopter lifts off from Kandahar Air Field at sunset in Kandahar, southern Afghanistan, November 19, 2007. REUTERS/Finbarr O'Reilly

According to the security officials, the incident took place near Angor Adda, a village in the tribal region of South Waziristan where officials have said U.S. commandos in helicopters raided a suspected al Qaeda and Taliban camp earlier this month.

“The U.S. choppers came into Pakistan by just 100 to 150 meters at Angor Adda. Even then our troops did not spare them, opened fire on them and they turned away,” said one security official.

While Angor Adda villagers and officials supported that account, the U.S. and Pakistani military denied the report.

Pakistan’s military spokesman Major Murad Khan confirmed there had been a shooting but said the American helicopters had not crossed into Pakistani airspace and Pakistani troops were not responsible for the firing.

Pentagon spokesman Bryan Whitman and a U.S. military spokesman in Afghanistan said American helicopters had not come under fire.

“I’ve checked into that and find it to be a spurious report,” Whitman told reporters. “Did not happen. I’ve checked all the places that would know about something like that and it doesn’t appear to be accurate.

“(I) cannot find any mission that correlates to the report I saw out of Pakistan. I can’t find any (military) report of helicopters being fired upon,” Whitman said.

Pakistan has been seen as an ally in the U.S. war on terrorism, and its support is key to the success of Western forces trying to stabilize Afghanistan.

But Washington has become impatient over Islamabad’s response to the threat from al Qaeda and Taliban fighters in Pakistan’s tribal regions. The United States has intensified attacks by missile-firing drone aircraft in recent weeks.

The New York Times reported last week that President George W. Bush has given clearance for U.S. raids across the border. The raid on Angor Adda on September 3 was the first overt ground incursion by American troops into Pakistan since the deployment of U.S. forces in Afghanistan in late 2001.

At least 20 people, including women and children, were killed in that South Waziristan raid, sparking outrage in Pakistan and prompting a diplomatic protest.

Pakistani army chief General Ashfaq Kayani said in a strongly worded statement last week that Pakistan would not allow foreign troops on its soil and Pakistan’s sovereignty and territorial integrity would be defended at all costs.

CONFLICTING VERSIONS

Official denials of the helicopter incident were contradicted by Pakistani civilian officials and villagers in Angor Adda.

One official told Reuters by telephone that “the troops stationed at BP-27 post fired at the choppers and they turned away.”

Two Chinook helicopters appeared set to land when troops began shooting, alerting tribesmen who also opened fire on the intruders, said a senior government official in Peshawar, the capital of North West Frontier Province.

A resident described the tension in the village through the night. “We saw helicopters flying all over the area. We stayed awake the whole night after the incident,” he said.

The fiercely independent tribesmen of the region carry weapons regardless of whether they are militants.

PAKISTAN ARMY FIGHTING MILITANTS

Despite U.S. frustration with Pakistan, its army has been involved in fierce fighting with Islamist militants in Bajaur, another tribal region, and Swat, a valley in North West Frontier Province, close to the tribal lands.

Pakistani forces, using helicopter gunships and artillery, killed at least 16 fighters and wounded 25 in Bajaur on Sunday. More than 750 militants have been killed in an offensive there that began in late August.

The U.S. pressure comes at an awkward time for President Asif Ali Zardari, widower of assassinated former prime minister Benazir Bhutto. Zardari was elected on September 6, having forced former army chief Pervez Musharraf to quit last month, almost nine years after he took power in a coup.

The new Pakistani president is in Britain to meet Prime Minister Gordon Brown to talk over the border situation.

Bush held a video conference with Brown last week to discuss a new strategy for the lawless Pakistan-Afghanistan frontier.

Zardari and Prime Minister Yousaf Raza Gilani have both endorsed the stand taken by General Kayani.