US aircraft flew over Kabul for the fourth night in succession yesterday as the Pentagon consolidated its command over Afghan airspace.
Anti-aircraft fire was reported over the capital as Taliban officials insisted their air defences remained in operation.
British defence sources described the attacks to date as limited and said they hoped the military action - so far tiny by comparison with the 1991 Gulf War and 1999 Kosovo campaigns - would trigger changes within Afghanistan.
In a demonstration of air superiority, US aircraft also made daylight sorties yesterday as they did on Tuesday, as Kabul reportedly suffered its heaviest bombardment since the US-led operation began on Sunday. Defence officials said they detected instability within the ruling Taliban regime.
In Washington, attention turned to the next stage of the campaign in Afghanistan, including US plans to use attack helicopters to seek out Taliban units as well as members of the al-Qaeda terrorist network. One strategic option focused on the use of Apache attack helicopters to protect special operations troops flying in Blackhawk helicopters.
Senior US officials have made clear special forces have already been on the ground in Afghanistan, conducting what is understood to be reconnaissance work.
US military planners are also preparing for the use of laser-guided bombs to attack bunkers where Taliban and al-Qaeda leaders may be hiding.
The Bush administration has repeatedly said that its target is to "smoke out" al-Qaeda leaders in order to target them once they come out of hiding.
However, military planners are also considering the option of suspending action, following the establishment of air superiority, while maintaining an air presence in case of opportunistic attacks. "We are engaged in something we can take our time to do," one said, adding that British efforts to grind down terrorist networks in Malaya, Oman and Northern Ireland had taken years.
Analysts suggested the Pentagon was preparing for a long period of air strikes as the US seeks out its targets. Anthony Cordesman, senior fellow at the Centre for Strategic and International Studies in Washington, said: "Barring a catalytic collapse of the Taliban, this could easily mean months of air strikes and a dissident-led ground campaign that could not be fully successful until next spring."
The United Nations said yesterday there were reports, which could not be independently verified, that 20 civilians were killed in Kabul and another 10 in Kandahar over three nights of strikes.
That sharply contrasts with higher estimates from Afghan media in Pakistan, where the Afghan Islamic Press reports 76 dead and more than 100 injured.
Meanwhile, as speculation continued on the next moves in the drive against terrorism, the British Prime Minister, Mr Tony Blair, moved yesterday to soothe simmering anxiety in the Islamic world that the United States is preparing to extend the bombing campaign against the al-Qaeda network and its Taliban allies to Iraq.
No steps will be taken against Iraq unless there is "absolute evidence" of complicity - which there is not, Mr Blair confirmed.
On his third diplomatic mission to shore up support for the global coalition against terrorism, Mr Blair took the unusual step of sanctioning what would, from anyone else, have been a highly sensitive leak.
After talks with Sultan Quboos, ruler of Oman, Mr Blair authorised a senior official to tell travelling journalists details of the official UK strategy drawn up by the Cabinet Office secretariat.
Among the insights it reveals is a belief that the opposition Northern Alliance lacks the resources to run the country unaided and also that Britain is determined that further military action is "compatible with international law and legitimate self-defence".
Coverage of the attacks on Afghanistan will continue throughout the day on Ireland.com's Response to Terror site at:
www.ireland.com/
special/usattack/