(AP) - The United Nations has put up blast walls around its main headquarters and closed some of its offices in Yemen because of security concerns in the country, U.N. and Yemeni officials said Sunday.
The changes, which include pulling out some nonessential staffers, follow an attack earlier this month on a housing complex for Western diplomats in Yemen's capital and a mortar attack last month on the U.S. Embassy.
Three mortars missed the American Embassy on March 20 but instead crashed into a high school for girls nearby, killing a security guard.
Three projectiles also hit a foreigners' housing complex in San'a on April 6, but caused no injuries. The complex is in an upscale neighborhood that also houses U.N. buildings.
A number of U.N. staffers at various agencies already have left Yemen, U.N. High Commission for Refugees' regional spokeswoman Abeer Etefa told The Associated Press by telephone from Cairo, Egypt.
She confirmed that some U.N. offices had closed but declined to elaborate. The UNHCR office remained open, Etefa said.
U.N. officials in Yemen were not immediately available for comment.
Ten-foot high blast walls and piles of sandbags have been put up around the United Nations' headquarters in San'a and Yemeni security troops were deployed around the building.
No employees have been seen entering or exiting the compound in several days, said a Yemeni security official, speaking on condition of anonymity because he was not authorized to describe the U.N. measures.
Yemeni security troops already protect foreign missions, hotels and U.N. buildings, he said.
After last month's mortar attack on the U.S. Embassy, several nonessential embassy employees left the country, according to a U.S. official who spoke on condition of anonymity because he is not authorized to talk to media.
The American Embassy has since issued a message urging citizens to exercise caution in areas of San'a where foreign companies have offices.
Yemen is a key U.S. ally in the Middle East but also the ancestral homeland of Osama bin Laden, and has been the site of violence against foreigners before.
Al-Qaida has an active presence in Yemen despite government efforts to destroy it. The group was blamed for the 2000 bombing of the USS Cole destroyer in the Yemeni port of Aden that killed 17 American sailors.