AC-130 gunships and A10 tankbusters, of the kind used in Iraq and Afghanistan, have been deployed by the US

The US has been giving the impression that it has backed away from the bombing campaign in Libya. It has now emerged that while the initial intensity of the high-altitude air strikes and cruise missile attacks has diminished, the US has not let up. In a dramatic and significant escalation of the assault on Gaddafi's forces, the US has deployed low-flying, heavily-armed aircraft against Libyan armour.

It is a deployment far removed from the initial concept of a "no-fly" zone.

The Pentagon has revealed that AC-130 gunships and A10 tankbusters, of the kind used in Iraq and Afghanistan, have been deployed in Libya. "We have employed A10s and AC-130s over the weekend," Vice-Admiral Bill Gortney, said.

The aircraft are better suited than high-flying fighter bombers to attack targets in built-up areas without so much risk of civilian casualties, defence officials say.

However, their sheer firepower can lead to civilian deaths as their attacks on the Iraqi city of Falluja after the 2003 invasion of Iraq demonstrated.

The AC-130 gunship is a heavily modified Hercules transport plane armed with 20mm, 40mm and 105mm cannons. The A10 "thunderbolts" conducts close-range attacks, notably against tanks and armoured vehicles. It is equipped with a multi-barrelled 30mm cannon which can fire a devastating almost 4,000 rounds a minute.

The use of the close air support aircraft has fuelled claims that the US is actively co-ordinating tactics with the rebels. Aware of the controversy any such admission could unleash, Gortney, director of the Pentagon's Joint Chiefs of Staff, said the US actions were in support of the UN-backed resolutions to protect Libyan civilians. "We're not in direct support of the opposition, that's not part of our mandate, and we're not co-ordinating with the opposition," he added. He described the US strategy as one of continuing "to pressure them where we think it's going to give us the best effect".

The AC-130s, flying from a base in Italy, were requested by General Carter Ham, the senior US general overseeing the operation, and are likely to continue flying over Libya in the coming days as allied forces attempt to increase the pressure on Gaddafi's ground forces, the Washington Post reported.

The RAF, which does not possess these low-flying US warplanes, has deployed Tornados firing laser or radar-guided weapons such as the Brimstone missile against Libyan armour. It has also fired Storm Shadow cruise weapons, costing an estimated £800,000 each, against ammunition bunkers in the Sabha area in the southern Libya desert.