Yemeni police have arrested five suspects over an attempted mortar attack on the U.S. Embassy in Yemen that mistakenly hit a nearby girl's high school, killing a security guard, an Interior Ministry official said Thursday.

Meanwhile, U.S. Embassy spokesman Ryan Gliha said that the embassy has informed its nonessential staff they are permitted to leave Yemen if they want to following the attack. The embassy said it will provide free flights to its voluntary staff who are not willing to remain in Yemen.

The Yemeni official said, speaking on condition of anonymity because he is not authorized to speak to the press, that the mortars in the attack appear to have been fired from the rooftop of a nearby building, rented by the attackers.

The official gave no further details about the attackers, their identities or their motivation for the attack.

U.S. State Department spokesman Tom Casey said on Tuesday that it was "fair to say that the embassy was a potential target." Washington "will be looking to work with Yemeni authorities as they investigate this incident," he said.

The Interior Ministry official initially suggested the attack might be linked to a dispute between a teacher and school administrators. The school had received a warning just two days earlier from the teacher's family, the official said.

The U.S. Embassy in Yemen, which is the ancestral homeland of Al Qaeda leader Usama bin Laden, has been the focus of violence before.

In March 2002, a Yemeni man lobbed a sound grenade into the embassy grounds a day after Vice President Dick Cheney made a stop for talks with officials at the San'a airport. The attacker, who allegedly sought to retaliate against 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 when 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 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 and an attack on a French oil tanker that killed one person two years later.