The Afghanistan theatre has been the first one, but it won't be the last - it is a place where you are setting an example for how this battle has to be conducted

Donald Rumsfeld

Mr Rumsfeld told the troops they were on the "front line between freedom and fear" and Afghanistan was "a proving ground" for future operations.

The BBC's Ben Brown, at the Bagram airbase near Kabul, says this is a strong hint that the Americans have Saddam Hussein's regime in Iraq in their sights.

Mr Rumsfeld refused to comment on reports of US special forces operating in Pakistan.

Raid

But reports from Pakistan say American and Pakistani troops have raided an Islamic school close to the Afghan border, in their first joint operation since the start of the war against the al-Qaeda network.

Local residents and Muslim clerics said about 200 Pakistani troops and 10 US soldiers stormed the school near Miram Shah, 250 kilometres south-west of Peshawar.

They said they failed to find any al-Qaeda fighters.

There are also reports of fighting between rival Afghan groups around Gardez, the capital of eastern Paktia province.

According to the Pakistan-based Afghan Islamic Press, forces loyal to Paktia warlord Padsha Khan launched an attack against the forces of the tribal council.

Rockets

In Kabul, sources from the International Security Assistance Force (Isaf) said the three rockets fired late on Friday night landed close to their base east of the airport.

Afghan and Allied soldiers keep the peace in Afghanistan's capital, Kabul

An Isaf spokesman said there was no damage to airport facilities and there were no casualties in the attack.

The US defence secretary is due to meet interim Afghan leader Hamid Karzai in Kabul.

Our correspondent in Kabul says the rocket attack and the regional clashes show that the security situation in Afghanistan is not completely under control.

Security fears

America and its allies' main concern in the region is an increase in guerrilla activities by Osama Bin Laden's al-Qaeda network and the Taleban in the coming months, as winter snows melt.

Mr Rumsfeld told journalists before arriving: "My guess is as spring comes and the weather improves they will try to communicate with each other, they will try to attack the interim authority as well as US and coalition forces."

Border hideouts

US, British and Afghan troops have continued to search caves and other al-Qaeda hideouts in Afghanistan, gathering weapons, documents and other materials left behind when enemy forces fled the area.

Many of the leaders of al-Qaeda and Afghanistan's former Taleban rulers are believed to be hiding in the rugged tribal north-west of Pakistan, able to travel between eastern Afghanistan and Pakistan through a mountainous border area impossible to seal off.

The US and UK governments have refused to confirm whether their troops are fighting in Pakistan, but if true it means a whole new front has opened in the war against terrorism.

Pakistan denial

"We do not characterise what other countries are doing or what we are doing in other countries," Mr Rumsfeld said.

But he did acknowledge that "agencies of the United States Government" were involved in the arrest last month in Pakistan of Abu Zubaydah, a senior lieutenant to Bin Laden.

Officials in Islamabad said on Thursday that the two countries share intelligence, but they denied that Pakistani forces were operating under the guidance of US advisers.