The Interior Ministry said that Qasim al-Raimi, described by Yemeni and foreign experts as a dangerous and experienced terrorist, had died with four of his lieutenants in a missile strike on their vehicles in Sa'ada province on Friday. It was not clear whether the attack was based on intelligence supplied by the US.

Analysts and diplomats say President Saleh is anxious to demonstrate speed and resolve in his pursuit of al-Qaida, above all to head off the hugely destabilising risk of US forces becoming visibly involved.

Apparent confirmation that al-Raimi has been killed will be seen as a significant setback for al-Qaida in the Arabian Peninsula, a merger of the Saudi and Yemeni branches of the group. Al-Raimi was one of 23 al-Qaida members who escaped from a Sana'a security prison in 2006, embarrassing the government and leading to suggestions of official complicity with the jihadis, a recurrent theme in the often tense relations between Yemen and the US.

Another of those reported killed was an Egyptian, Ibrahim Mohammed Saleh al-Banna, the group's ideologue.

Yemeni government sources said three other al-Qaida fighters were captured on Saturday near the Saudi border with weapons, explosives and leaflets, the 26September.net website reported.

Yemen announced last week that it was waging "all-out" war on al-Qaida, as conservative clerics warned they would wage "jihad" against any foreign forces. The US and Britain say they are financing and training Yemeni counter-terrorist and coastguard units, but there are indications of deeper US involvement. New security measures are being put in place at sensitive installations all over the country.

President Obama has made it clear that he does not plan to send ground forces to Yemen, which is facing a civil war in the north and separatists in the south, as well as grinding poverty, unemployment and illiteracy.

Yemen has claimed that Umar Farouk Abdulmutallab, the Nigerian "pants bomber" in the Christmas Day incident, was radicalised while studying in London. But the US and Britain say they are concerned about the proliferation of "ungoverned spaces" in Yemen in which al-Qaida can train and operate. President Saleh clearly wants to show that he is taking the initiative in advance of the conference Gordon Brown has convened in London on 27 January to galvanise international support for Yemen.

Yemen has meanwhile tightened security measures along its Red Sea coastline in response to threats from the al-Shabaab movement in Somalia that it will send fighters to support al-Qaida, ­al-Arabiya TV reported.