Kabul, Afghanistan (CNN) -- Part of the U.S. embassy annex in Kabul came under attack early Monday, a U.S. official and an official from the International Security Assistance Force said.
The attack was believed to be largely over by about 4 a.m., the U.S. official said. At that point, there was not yet any word on casualties.
ISAF Maj. Jason Waggoner said it was a single incident, not several attacks.
The U.S. official described the situation as fluid at the targeted facility, which is used by U.S. government personnel in the Afghan capital.
The area is known as a place where personnel both live and work, some in intelligence operations. A CIA spokeswoman declined to comment on the attack.
"Police have heard gunshots in the area," said Siddiq Siddiqi, the spokesman for the Afghan interior ministry. "The gunshots continued for three or four minutes."
Afghanistan has been site of several high-profile attacks of late, including strikes at the NATO headquarters and the U.S. Embassy in Kabul and the assassination of former Afghan President Burhanuddin Rabbani. Rabbani had been leading efforts for reconciliation talks.
U.S. Secretary of Defense Leon Panetta contended last Thursday that such attacks represent a strategy shift by the Taliban, the conservative and militant group that has been waging a years-long fight in the war-torn nation.
"We judge this change in tactics to be a result of a shift in momentum in our favor and a sign of weakness in the insurgency," Panetta said in a Senate Armed Service Committee hearing.
He added that "the insurgency has been turned back in much of the country, including its heartland in the south, and Afghan National Security Forces are increasingly strong and capable."
Mike Mullen, the outgoing chairman of the Joint Chiefs of Staff, testified then that he felt Pakistan is "exporting" violence to Afghanistan. He described the Haqqani terrorist network as "a veritable arm of Pakistan's intelligence" -- an assertion that Pakistani officials later strongly denied, even as it admitted the country does have contacts with the group.
August was the deadliest month for U.S. forces in Afghanistan since the conflict began. Seventy-one American troops died that month, including 30 killed when insurgents shot down a helicopter August 6 in the eastern central province of Wardak.
The surge in U.S. deaths comes as NATO is drawing down and handing over security control to national forces. Some 10,000 U.S. troops are scheduled to depart by year's end, with all U.S. military personnel out of Afghanistan by the end of 2014.
CNN's Barbara Starr and Claudia Dominguez contributed to this report.