A spokesman for the new alliance, his face blacked out, made the announcement on a video broadcast by al-Jazeera. He described the alliance as "the political council of the Iraqi resistance".

The six Sunni groups have been in discussion about the move for months. The aim is to reduce the fragmented nature of the insurgency but also to try to claim a slice of the political agenda after the expected US withdrawal.

The talks about the alliance were disclosed by the Guardian in July. The groups had been close to making an announcement at that time but delayed because of disagreements over how to respond to the US policy of doing deals with Iraqi tribal leaders.

In a lengthy statement published yesterday, the six groups listed a 14-point political programme, of which the first was continued action against US forces. "The occupation of Iraq is an act of aggression and an act of gross injustice which is rejected Islamically, legally and rationally, and which all laws grant the right to oppose and resist," it said.

It declared all laws passed by the Iraq government null and void.

The six groups are opposed to al-Qaida in Iraq, which has been behind some of the most spectacular and bloodiest attacks, often on civilians, tactics that have alienated large swaths of the Iraq population. The main reason for the partial success of the US deals with local leaders, initially in Anbar province, is hostility towards al-Qaida.

The six groups in the alliance are the Islamic Army in Iraq, the al-Mujahideen Army, Ansar al-Sunna, al-Fatiheen Army, the Islamic Front for the Iraqi Resistance (Jami), and Iraqi Hamas.

One of the biggest groups, the 1920 Revolution Brigades, had been involved in the discussions but pulled out. A spokesman for the brigades said it had not joined the alliance because it did not want to clash with those Sunni tribal groups working with the US against al-Qaida. "We will give time to people who have been harmed by al-Qaida and its violence," he told the Guardian. He denied an Economist report that the 1920 Revolution Brigades was working with the Americans. On the contrary, the group continued to attack US troops.

The new political alliance does not recognise the government led by Nuri al-Maliki. In its 14-point plan it says that all laws and treaties agreed under the occupation would be rescinded. The statement also claimed that the country would not be ruled by a "single element" that represented any ethnic or sectarian interest, presumably a reference to the Shia Muslim-dominated government.

One of the main features of the insurgency has been its fragmented nature, with diverse groups, large and small, operating largely independently.

Even with the new alliance there are still huge splits. Outside the alliance are not only al-Qaida and the 1920 Revolution Brigades but some Sunni groups. Also operating in Iraq are the Shia Muslim militia groups such as the Mahdi army, which has declared a six-month ceasefire, and the Badr brigades.