Yemen has launched an offensive against al Qaeda and the US embassy in Sanaa reopened on Tuesday after security forces staged a raid just outside the capital that dealt with an imminent security threat.

Yemen has sent thousands of troops to take part in a campaign against al Qaeda in three provinces over the past three days, and they are hemming them in, security sources said. Five suspected fighters from the group were detained, they said.

'The campaign is continuing in the capital and in the provinces of Shabwa and Maarib,' one source told Reuters, on condition of anonymity. The manhunt was also going on in the southern province of Abyan. There were no further details.

The US embassy in Yemen said it reopened after a raid that killed two al Qaeda militants dealt with specific security concerns which had forced US and European missions to close.

Yemen, the poorest Arab country, was thrust into the foreground of the US-led war against Islamist militants after a Yemen-based wing of al Qaeda said it was behind a Christmas Day bomb attempt on a US-bound plane.

US Secretary of State Hillary Clinton has said fighting in Yemen was a threat to regional and global stability.

'Successful counter-terrorism operations conducted by Government of Yemen security forces ... have addressed a specific area of concern, and have contributed to the embassy's decision to resume operations,' the US embassy said.

It said in a statement that the mission, a fortified structure with concrete slabs to guard against attacks, had closed for two days on credible information on the 'likelihood of imminent terrorist attacks in the Yemeni capital.'

High security

Yemen increased security measures around embassies and residential areas where foreigners live, state media said. Twin suicide car bombs killed 16 outside the US mission in 2008.

'The Ministry of Interior emphasizes that all embassies, diplomatic missions and foreign companies are fully secured and there is nothing to be worried about,' a ministry source told the state news agency.

Yemeni forces killed at least two al Qaeda militants on Monday they said were behind threats that forced embassies to close, and President Ali Abdullah Saleh said Yemen would defeat anyone thinking of harming the country and its security.

Yemen, with shrinking oil reserves, a water crisis and fast-growing population, had already stepped up security on its coast to block militants from reaching its shores from Somalia.-Reuters