Kabul, Afghanistan (CNN) -- Five U.S. soldiers were wounded Thursday when a suicide bomber attacked a U.S. base, an Afghan official said.
The attacker detonated the bomb about 9 p.m. while in the "sleeping area" on the base, said Paktia province spokesman Roullah Samoun. It is unclear how the bomber got onto the base, but preliminary investigations show the attacker wore an Afghan border police uniform, Samoun said.
NATO's International Security Assistance Force said that "several ISAF service members from the United States were injured" in an explosion on their base in eastern Afghanistan's Paktia province. The assistance force did not confirm that the explosion was caused by a suicide bomber.
There was no immediate word on the extent of damage.
An earlier suicide attack on a U.S. base in Afghanistan killed seven CIA officers and a Jordanian army captain on December 30. The Pakistani Taliban claimed responsibility for the attack, also on a base in eastern Afghanistan.
Former CIA official Robert Richer called the bombing the most loss of life for the agency since the 1983 bombing of the U.S. Embassy in Beirut, Lebanon, in which eight agents died.
CNN's Frederik Pleitgen contributed to this report.