An apparent mortar attack smashed windows at a complex housing Americans and other Westerners in the Yemeni capital Sanaa on Sunday, but there were no casualties, a Yemeni security official said.

"There were three blasts believed to have been caused by mortar shells. There is broken glass, but no casualties," the official told Reuters, adding that the unknown attackers escaped.

Residents said earlier they saw police arriving outside the high-security area in the southwest of the capital of the poor Arab state, which has been the scene of frequent attacks by Islamic militants, disgruntled tribesmen and Shi'ite rebels.

An al Qaeda-linked group claimed responsibility for a failed mortar attack on the U.S. embassy in Yemen last month that wounded girls at a nearby school and a group of soldiers.

The U.S. State Department offered free flights out of Yemen to non-essential diplomats and family members after the attack.

The group had earlier claimed responsibility for deadly attacks on Spanish and Belgian tourists in the Arabian Peninsula country.

Yemen, the ancestral home of al Qaeda leader Osama bin Laden, is viewed in the West as a haven for Islamic militants, dozens of whom are jailed for involvement in bombings of Western targets and clashes with authorities.

The oil-producing country joined U.S.-led efforts to fight terrorism after the Sept. 11, 2001, attacks on U.S. cities and has itself witnessed a number of attacks targeting foreign tourists, oil installations, and U.S. and French ships.

Yemen is one of the world's poorest outside Africa, and a 2007 World Bank report noted domestic production of crude oil had declined steadily since 2001. Poverty and unemployment are fuelling discontent in parts of the country.