The MoD repeatedly denied Mark 77 incendiary bombs were dropped, on the basis of US assurances. Defence secretary John Reid now says the assurances, made to predecessor Geoff Hoon, were wrong and he "must correct the position".

US Marines dropped 30 Mark 77 fire bombs between March 31 and April 2 2003 "against military targets away from civilian areas". In a letter to Michael Ancram, shadow defence secretary, Mr Reid also says: "The MK77 does not have the same composition as napalm, although it has similar destructive characteristics."

He adds the Pentagon had also told the government that "owing to the limited accuracy of the MK77, it is not generally used in urban terrain or in areas where civilians are congregated". Mr Reid points out Britain is bound by convention not to use incendiary weapons against military targets located within concentrations of civilians.

He continues: "US policy in relation to international conventions is a matter for the US government, but all of our allies are aware of their obligations under international humanitarian law."

Mr Ancram said the issue raised questions "about the quality of our communications with our US allies", and has asked Mr Reid to explain.

He also referred to an article in August 2003, Officials confirm dropping firebombs on Iraqi troops, in the San Diego Tribune, which said Marine pilots dropped dozens near bridges, creating fireballs.

Mr Hoon was denying the use of incendiary bombs, on the basis of what he was told, as late as April this year.

When reports surfaced, the Pentagon separated "napalm" from "firebombs". According to GlobalSecurity.org, MK77s "function identical to earlier MK77 napalm weapons" using kerosene rather than benzene.