The death of a rebel military commander proves that Britain has made a mistake by recognising the National Transitional Council as the "sole governmental authority" in Libya, according to Colonel Muammar Gaddafi's regime.
Tripoli said the killing of General Abdel Fattah Younes, a former government minister who defected to the rebels, was "a nice slap to the face" of the UK and proof the NTC could not rule Libya.
Mystery still surrounds the death of General Younes, who was shot earlier this week.
Rebels claim the commander and two aides were killed by gunmen after being recalled from the front.
While the Gaddafi regime said al Qaida - a group its claims is the strongest force within the rebel movement - was responsible.
Government spokesman Moussa Ibrahim told reporters: "It is a nice slap to the face of the British that the council that they recognised could not protect its own commander of the army.
"By this act, al-Qaeda wanted to mark out its presence and its influence in this region.
"The other members of the National Transitional Council knew about it but could not react because they are terrified of al Qaida."
The general joined the rebels at the beginning of the Libyan uprising in February. He had served at the heart of Gaddafi's regime since the 1969 coup.
Foreign Secretary William Hague announced Britain was recognising the NTC on Wednesday following similar moves by France and the US.