Douglas Hurd, the Foreign Secretary, said in Tokyo that Baroness Thatcher was not the only person to suggest arming the Serbs: 'Other people have looked at the option and may look at it again.'
But ministerial sources said that air strikes would become possible only if the Owen-Vance peace plan collapsed and fighting on the ground halted UN humanitarian aid convoys.
The allies are holding out against public pressure for more immediate action in the hope that in a fortnight in the UN Security Council Russia will support tightening of sanctions against Serbia.
British ministers said a proposed 15-day postponement of the sanctions would be dropped and they would be imposed immediately they were agreed to compensate for the delay in waiting for the Russian referendum on Boris Yeltsin's leadership on 25 April.
Lady Thatcher's acerbic criticism of the Western response, which she reinforced in the House of Lords and television broadcasts in the United States yesterday, appeared to have struck a chord with politicians and public.
Although ministers said that her call to arm the Muslims would only deepen suffering, her attack provoked a Commons statement by Malcolm Rifkind, the Secretary of State for Defence.
He attempted to hold the line against support for her call by MPs from all sides; Tory MPs spoke of the 'shame' of the West's apparent inability to halt the suffering.
Mr Rifkind said the clear military advice to the Government was that air strikes unsupported by substantial numbers of ground troops would be unlikely to be effective given the nature of the conflict, weapons deployed, and terrain. The chances of civilian casualties would be high.
He added: 'While one should not rule out this expedient absolutely, it is one which would change in a fundamental way, the role of the UN and bring them into the heart of the conflict as a combatant.' He left open the possibility of air strikes on targets which could be properly identified.
Defence sources said that did not include the heavy artillery shelling Srebrenica because they could be hidden. Possible targets could include Serbian supply lines, but ministers insisted such strikes would not solve the conflict.
In Tokyo, Mr Hurd appeared to take a harder line on Serbia, demanding that sanctions be imposed within the next two weeks. According to a British aide, G7 ministers have decided to overcome Russian objections in the Security Council and isolate the Serbs for their continuing atrocities in Bosnia. 'The G7 is agreed on sanctions this month,' he said. 'We cannot mess about forever.'
The British official denied that any G7 aid package for Moscow would be directly linked to co-operation over sanctions - but made it clear that the issues were related. 'We are here talking about aid, but we will be making that point on foreign policy (about Serbia) forcibly.'
In Belgrade, the US special envoy, Reginald Bartholomew, delivered a blunt warning to the Bosnian Serbs that if they did not sign the Owen-Vance peace plan, the US would back lifting the arms embargo on Bosnian Muslims.
The Bosnian Serb leader, Radovan Karadzic, appeared unmoved by the threat, saying the Serbs would break off talks if the world community continued to pressure Serbs to sign the plan. Last night, Serbs resumed the shelling of Srebrenica - wounding six civilians.
Should we use force? page 7
Death of a town, page 10
Leading article, Letters, page 23
No more troops, page 25
Andrew Marr, page 25Reuse content