SANAA - Yemen has launched an offensive against al Qaeda and the U.S. 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 U.S. embassy in Yemen said it reopened after a raid that killed two al Qaeda militants dealt with specific security concerns which had forced U.S. and European missions to close.

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

U.S. 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 U.S. 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.

Placed strategically on the Arabian Peninsula's southern rim, Yemen is trying to fight a threat from resurgent al Qaeda fighters while a Shi'ite revolt rages in the north and separatist sentiment simmers in the south.

The West and Saudi Arabia fear al Qaeda will take advantage of Yemen's instability to spread its operations to the neighboring kingdom, the world's biggest oil exporter, and beyond. Yemen itself produces a small amount of oil.

The British and French embassies also resumed operations on Tuesday but remained closed to the public, diplomats said.


INCREASED SECURITY

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

Nevertheless, the threat of terrorist attacks against American interests remains high and the embassy continues to urge its citizens in Yemen to be vigilant and take prudent security measures, the U.S. mission said.

Yemeni officials acknowledge the need for U.S. help with counter-terrorism, but say the government also lacks resources to tackle the poverty that widens al Qaeda's recruiting pool.

Defense and counterterrorism officials say Washington has quietly been supplying military equipment, intelligence and training to Yemen to root out suspected al Qaeda hide-outs.

The Christmas Day bombing attempt has put a spotlight on the growing prominence of al Qaeda in Yemen and the expanding role of the U.S. military and spy agencies in fighting the group.

Civil war and lawlessness have turned Yemen into an alternative base for al Qaeda, which U.S. officials say has been largely pushed out of Afghanistan and is under military pressure from the Pakistani army in bordering tribal areas.

Yemen has been a long-standing base of support for al Qaeda. Militants bombed the Navy warship USS Cole in the Yemeni port of Aden in 2000, killing 17 U.S. sailors. And Yemenis were one of the largest groups to train in al Qaeda's camps in Afghanistan before the September 11 attacks in 2001.

Violence also flared in the Yemen-Saudi border area, where Shi'ite rebels waging a revolt against the central government said a series of Saudi air strikes on a market had flattened shops and homes, killing two people and wounding three more.

Shi'ite rebels from the Zaidi sect in northern Yemen have fought government troops since 2004 in a conflict that has killed hundreds and displaced tens of thousands, complaining of social, economic and religious marginalization.

The conflict drew in Saudi Arabia in November when rebels made a cross-border incursion into the world's top oil exporter.

(Reporting by Mohamed Sudam in Sanaa, Cynthia Johnston in Dubai and Jim Loney in Baghdad; Writing by Cynthia Johnston; editing by Thomas Atkins/Peter Millership)

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