Islamabad, Nov 26: At least 28 Pakistani soldiers were killed today when NATO helicopters and combat jets fired on two border posts in the country's northwest, prompting army chief Gen Ashfaq Parvez Kayani to direct his troops to prepare for "an effective response" even as authorities cut off all supplies for US forces in Afghanistan.
The attack, the worst single incident of its kind in one decade, looked set to plunge US-Pak relations, already deeply frayed, further into crisis.
A major and a captain of the Pakistan Army were among those killed when NATO aircraft fired at the borders posts in Baizai area of Mohmand tribal region at 2 am.
Fifteen more personnel were wounded and the death toll could rise as some of the injured were in a serious condition, several officials said.
A military statement said the NATO aircraft "carried out unprovoked firing" on the border posts. Pakistani troops "effectively responded immediately in self-defence to NATO/ISAF's aggression with all available weapons".
Gen Kayani strongly condemned "NATO/ISAF's blatant and unacceptable act".
While lauding the effective response by Pakistani soldiers, he issued orders for taking all necessary steps for "an effective response to this irresponsible act".
Within hours of the attack, Pakistani authorities sealed off the country's border stopping all container trucks and tankers carrying supplies for US and NATO forces in Afghanistan.
Foreign Secretary Salman Bashir called in US Ambassador Cameron Munter to lodge a "strong protest on the unprovoked NATO/ISAF attack", the Foreign Office said in a statement.
Bashir told the US envoy that the attack had "deeply incensed the government and the people of Pakistan".
The President, Prime Minister and the government "strongly condemn the attacks which were totally unacceptable, constituted a grave infringement of Pakistan's sovereignty, were violative of international law and a serious transgression of the oft conveyed red lines", the statement said.
The incident could have "serious repercussions on Pakistan-US/NATO/ISAF cooperation", the statement further said.
Prime Minister Yousuf Raza Gilani described the incident as an "attack on Pakistan's security and sovereignty" and cut short a visit to his hometown of Multan to rush back to Islamabad.
He convened a meeting of the Defence Committee of the Cabinet to formulate Pakistan's response to the incident.
US Ambassador Cameron Munter expressed regret at the incident and offered assistance in probing it.
In a statement issued by the US embassy, Munter said: "I regret the loss of life of any Pakistani servicemen, and pledge that the United States will work closely with Pakistan to investigate this incident."
The Pakistani military said in a statement that International Security Assistance Force (ISAF) and NATO helicopters "carried out unprovoked and indiscriminate firing" on the Pakistani check post.
A spokesman for the NATO-led ISAF in Kabul said the coalition was aware of "an incident" near the border and was gathering information on it.
Security forces blocked all entry points to Mohmand tribal agency after the incident and began checking all vehicles, TV news channels reported.
Several crossings on the Afghanistan frontier, including Landikotal and Takhtbai, were closed and over 150 NATO supply vehicles sent back to Peshawar.
The Pakistani embassy in the US lodged a verbal protest over the attack.
Deputy Chief of Mission Iffat Gardezi contacted the US State Department at midnight and described the incident as "unprovoked".
Pakistan's Ambassador to the European Union Jalil Abbas Jilani lodged a similar protest with NATO.
Former premier Nawaz Sharif, the chief of the PML-N, condemned the incident and described it as an "act of terrorism" while Pakistan Tehrik-e-Insaf chief Imran Khan called on the government to pull out of the US-led war on terrorism.
The incident occurred just a day after Pakistan army chief Gen Ashfaq Parvez Kayani and the commander of coalition forces in Afghanistan, Gen John Allen, met in Islamabad and discussed the need for tighter measures to block the movement of militants across the Pakistan-Afghanistan border.
Kayani and Allen "discussed measures concerning coordination, communication and procedures between Pakistan army, ISAF and Afghan army aimed at enhancing border control on both sides", an army statement said.
On today's incident, Gen Allen said NATO will "thoroughly investigate" it.
"This incident has my highest personal attention and my commitment to thoroughly investigate it to determine the facts," Allen said in a statement in Kabul.
In May, two Pakistani soldiers were injured in an exchange of fire with two NATO helicopters from Afghanistan that intruded into the volatile North Waziristan tribal region.
Pakistan had retaliated against yet another incursion by NATO helicopters in September last year, which killed two Pakistani soldiers, by shutting down the main supply route for NATO forces.
The route was reopened after the US tendered an official apology for the incursion.

Lastupdate on : Sat, 26 Nov 2011 21:30:00 Makkah time
Lastupdate on : Sat, 26 Nov 2011 18:30:00 GMT
Lastupdate on : Sun, 27 Nov 2011 00:00:00 IST