(Adds Belgian comments, Yemeni official on al Qaeda)

By Mohamed Sudam

SANAA, Jan 18 (Reuters) - Gunmen opened fire on a group of tourists in Yemen on Friday, killing two Belgian women and their two Yemeni drivers and wounding two other people, Yemeni officials said.

The attack came less than a week after al Qaeda's wing in Yemen vowed to act to win the release of jailed Islamic militants. Belgian officials quoted Yemeni authorities as saying they believed al Qaeda was behind Friday's attack.

"There were apparently four terrorists who ambushed two tourist vehicles," Taha Hajer, governor of the eastern Hadramout province, told Reuters.

"The search for the attackers is intensifying and checkpoints have been set up throughout the province."

Helicopters joined the hunt for the unidentified gunmen, a security official said.

The tour group was flown along with the bodies of the dead Belgians to the capital Sanaa after the attack, in which a Belgian tourist and a Yemeni were wounded, Hajer said.

In July, a suicide bombing killed seven Spanish tourists and wounded six at the Queen of Sheba Temple, built around the 10th century BC. Two Yemenis were also killed.

The ancestral home of al Qaeda leader Osama bin Laden, Yemen joined the U.S.-led war on terrorism after al Qaeda's Sept. 11, 2001 attacks on U.S. cities.

It has experienced several militant attacks and kidnappings of tourists by disgruntled tribesmen, and is viewed in the West as a haven for Islamic militants.

AL QAEDA

In an Internet posting last week, al Qaeda's wing in Yemen vowed to free its prisoners from the country's jails and retaliate for the government's killings of militants. Officials said last year that the July attack had been preceded by an al Qaeda demand for the release of jailed comrades.

"By God we shall not rest ... until we free our brothers and sisters from the prisons," the group said in an e-magazine posted on an Islamist Web site on Jan. 12. "The Prophet (Mohammad) ... has ordered that we free detainees."

Dozens of al Qaeda militants are serving jail terms in Yemen for involvement in bombing attacks on Western targets and clashes with the authorities.

A Yemeni official told Reuters, of Friday's attack: "We do not dismiss al-Qaeda's involvement, considering the style of the attack and the group's frequent threats against foreign interests in the region."

Belgian Foreign Minister Karel de Gucht was horrified by the attack and had sent a "clear message" to the Yemeni government to hunt down the killers, Belgium's Foreign Ministry said in a statement.

One of the poorest countries outside Africa, Yemen, on the Arabian peninsula, has been trying to attract tourists put off by kidnappings and bomb attacks and boost foreign investment as its oil dwindles.

In November Yemen jailed 32 suspected militants over two foiled suicide attacks on oil and gas installations in 2006, days after al Qaeda urged Muslims to attack Western interests. All the defendants pleaded not guilty and six said they had been tortured.

Al Qaeda's wing in Yemen claimed responsibility for the foiled raids and vowed to carry out more attacks. (Writing by Firouz Sedarat, editing by Andrew Roche)

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