KABUL, Afghanistan (AP) -- Suicide bombers struck two government offices in southern and western Afghanistan on Tuesday, killing 16 people as militants step up attacks across the country with the arrival of spring temperatures, authorities said.
Insurgents have been targeting Afghan and NATO security forces as they fight to assert their power and undermine U.S. efforts to try to build up Afghan forces. Afghanistan's police and army are increasingly shouldering the job of providing security with the planned exit of most foreign combat troops by the end of 2014.
The Taliban claimed responsibility for both attacks -- one in the western region of Herat and the other in the southern province of Helmand -- in telephone messages to the media.
The deadliest bombing occurred in Herat when a sport utility vehicle packed with explosives blew up outside the gate of the Guzara district police office as people were waiting to go inside to see government officials about various business matters.
Raouf Ahmedi, a spokesman for the police commander of the western region of Afghanistan, said police in the area had received a tip that the black four-wheel-drive vehicle was loaded with explosives.
"They were chasing the car and tried to stop it," Ahmedi said. "The vehicle then turned toward the district headquarters building and tried to pass the checkpoint, but police stopped them to be searched and asked where they were going."
Moments later the vehicle exploded, causing a loud boom that could be heard a few miles away. Two men and a woman wearing a burqa were found dead inside the vehicle, officials said.
"The explosion was so strong -- there are casualties among police and civilians," said Nasar Ahmad Popul, the chief of the province's Guzara district who was inside the headquarters at the time of the blast.
Popul said three security officers and nine civilians were killed, and more than 50 people, including children, were wounded.
Barriers at the blast site were blackened and investigators examined charred remains of what was left of the vehicle. Several of the wounded were loaded onto the back of police pickup trucks and taken to a hospital. Rescue workers wrapped those killed in white sheets and carried them from the site.
Herat province, as well as most of western Afghanistan, has been relatively calm as insurgents have concentrated their attacks in the country's south and east. The responsibility for nearly all of Herat province has been transferred, or is in the process of being transferred, from NATO troops to Afghan forces.
Later Tuesday, three suicide attackers wearing explosives-laden vests parked their car outside a police station in the Musa Qala district of the southern Helmand province, then walked toward the entrance, said Daoud Ahmadi, a provincial spokesman.
Police fired at the attackers, killing one. Two others blew themselves up inside the compound, Ahmadi said. He initially reported that eight policemen died but later revised the toll, saying that four policemen were killed and five, including the district commander, were wounded.
Associated Press Writer Deb Riechmann in Kabul contributed to this report.