The war on terror "is not a classical war"
International Development Secretary Clare Short stressed that any action by land forces in the war against terror would be very carefully targeted.
She repeated her insistence that "swarms and swarms of troops all over Afghanistan" would not happen.
Her comments came after British armed forced provided support for a sixth night of US-led military strikes on Friday.
Ms Short told BBC Radio 4's Today programme on Saturday that the war on terror was "not a classical war".
"There isn't going to be a mass land invasion. There will be some activity," she said.
She added that the bombing in Afghanistan should be limited to "targets protecting the Taleban's protection of the al-Qaeda network".
'Get UN involved'
"The UK Law Offices look at every target that is proposed.
"There have to be targets that you need bombing, in order to attack those targets for it to be legal."
Liberal Democrat leader Charles Kennedy said he wanted to see the United Nations involved in the crisis as soon as possible.
He reaffirmed his backing for the military action, but said he believed the UN could play a vital role in bringing stability to Afghanistan.
"The United Nations is probably going to prove to be the most effective body to go in and basically to pick up the pieces, and that will probably, I suspect, take the form of some kind of UN protectorate," he said.
Logistical support
The US air raids on Afghanistan resumed early on Saturday after being suspended on Friday for the Muslim weekly day of prayer.
Eyewitnesses in Kabul reported at least four explosions in two separate raids, with at least one bomb hitting the airport.
A Ministry of Defence spokesman said British forces were involved in coalition activities but only in a support role.
Britain is so far the only country other than the US to have participated in the attacks on Afghanistan.
Its submarines were involved in missile firing on the first night of the campaign.
But since then their role has been restricted to refuelling planes and other support work.
Afghan aid
Ms Short said on Saturday that mass starvation in Afghanistan could be prevented if international food programmes could send sufficient supplies to Afghanistan before winter.
It follows her comments on Friday that aid workers were facing a "race against time" to prevent a massive humanitarian crisis in the south Asian country.
Britain has pledged an extra £15m, in addition to £25m already committed, to assist aid efforts in the region.
Ms Short told Today: "It was a thousand metric tonnes yesterday and it is going to be something like that tomorrow.
"That is the kind of level we have got to keep up for the next five weeks, both to get people fed now and to stock up the warehouses so Afghanistan can get through the winter, when the roads will be much more difficult to move food across."