At least two Americans and two Pakistani soldiers and were wounded.

Meanwhile, strikes called by opposition parties brought Karachi and other cities to a standstill yesterday as gunmen killed a top court official in further violence over the suspension of Pakistan's top judge.

Maj. Gen. Waheed Arshad said "miscreants" -- usually a byword used by Pakistani officials to describe Islamic militants -- fired at the convoy carrying military officials who attended a meeting in the northwestern town of Teri Mangal.

Afghan military officials also attended the talks to discuss recent fighting between Afghan and Pakistani forces that the government in Kabul says has killed at least 13 people inside Afghanistan -- inflaming already poor relations between Pakistan and Afghanistan.

NATO's International Security Assistance Force in Afghanistan said it could confirm ISAF casualties but not the exact number of injured or killed.

Maj. William Mitchell, a spokesman at the US military base in Bagram, Afghanistan, said officials were trying to verify conflicting reports of violence.

Rahmatullah Rahmat, governor of the Afghan border province of Paktia, said that he, US military advisors and Afghan army leaders traveled by helicopter to Pakistan for the meeting.

He said that after the meeting finished, gunmen opened fire on the group as they were heading toward their helicopters. Rahmat reported two American dead and two wounded.

He said that American soldiers returned fire.

In Karachi, shops and schools were closed while most public transport remained off the streets, a southern commercial hub where nearly 40 people were killed at the weekend in clashes between pro- and anti-government supporters.

The violence erupted on Saturday after pro-government activists blocked Chief Justice Iftikhar Muhammad Chaudhry from addressing a public rally following his suspension on March 9 by President Pervez Musharraf.

Authorities in the volatile port city, Pakistan's biggest metropolis with a population of more than 12 million people, said in a statement they had called a public holiday to "mourn the deaths of those killed."

Sporadic unrest spilled into a third day in several parts of Karachi as angry protesters fired in the air, burnt tyres and blocked roads overnight, witnesses said, although there were no reports of casualties.

Police said they found the bullet-riddled body of a man in a large sack in the city's port area Monday.

Troops were ordered to shoot rioters on sight in Karachi on Sunday and authorities also banned gatherings of more than five people in the city to prevent further trouble.

Sindh province interior secretary Brigadier Ghulam Muhammad Muhtaram said that authorities intend to expel some opposition leaders from the city, although names have not been finalised.

Karachi police official Faqir Ahmed said there was a "very tense situation" because ethnic clashes had now developed between Pashtuns originally from the Afghan border area and people whose families emigrated from India after 1947.

Most of the eastern city of Lahore was also shut down by a strike while lawyers boycotted courts, witnesses said.

Around 2,500 protesters in Lahore hanged and burned effigies of Musharraf and of Altaf Hussain, the exiled leader of the pro-Musharraf Muttahida Qaumi Movement which was involved in the Karachi clashes.

The strike also paralysed North West Frontier Province bordering Afghanistan including the provincial capital Peshawar, witnesses and officials said.

In Islamabad gunmen broke into the house of Syed Hamad Raza, the deputy registrar of the Supreme Court, and shot him dead early Monday in what his family said was a killing linked to his role at the court.

His brother Khalid Ali Shah dismissed initial police reports he was killed by robbers. "It was a targeted killing, it was not a robbery... We need justice."

Chaudhry visited the site of the killing yesterday. Security officials said Chaudhry had brought Raza to Islamabad with him from the southwestern city of Quetta after he was appointed to lead the Supreme Court in 2005.