Three mortar rounds targeting the U.S. Embassy in Yemen crashed into a girls high school next door, killing a security guard and wounding 13 girls on Tuesday, officials said.

The U.S. State Department said embassy officials had concluded that the attack was "directed against our embassy." U.S. officials refused to comment further, saying it was still under investigation.

The embassy issued a statement in Arabic saying none of its employees was wounded, adding that "we pray for the victims and their families." The embassy closed for the rest of the day.   

A statement from the Yemen Interior Ministry said the shells fired by unidentified attackers in a downtown district of the capital city of Sana'a wounded five soldiers and 13 girls. The conditions of three of the girls were described as serious and they were being flown to Jordan for treatment.

The statement did not mention the death of the guard, which was reported by a ministry official who spoke on condition of anonymity because he was not authorized to talk to the press.

"The ministry will arrest those terrorists as fast as it can and bring them to justice," the ministry statement said.

Troops sealed off roads and prevented journalists from approaching the school, which is attended mostly by Yemeni students.

Embassy attacked before

The U.S. Embassy in Yemen has been the focus of violence before.

In March 2002, a Yemeni man lobbed a sound grenade into the embassy grounds a day after U.S. Vice-President Dick Cheney stopped at the Sana'a airport for talks with officials.

The attacker, who allegedly sought retaliation for what he called American bias toward Israel, was sentenced to 10 years in prison, but the sentence was later reduced to seven years.

In March 2003, two people were fatally shot and dozens more were injured as police clashed with demonstrators trying to storm the embassy as tens of thousands rallied against U.S.-led invasion of Iraq.

In 2006, a gunman opened fire outside the embassy but was shot and arrested by Yemeni guards. The gunman, armed with a Kalashnikov rifle, claimed he wanted to kill Americans.

Al-Qaeda has an active presence in Yemen, with leader Osama bin Laden calling the country his ancestral homeland.

Yemen's government has tried to crack down on al-Qaeda, a group blamed for the 2000 bombing of the USS Cole destroyer in the Yemeni port of Aden that killed 17 American sailors, and an attack on a French oil tanker that killed one person two years later.