In other violence, militants fatally shot two police officers in the south, where four suspected Taliban were killed in a clash with NATO and Afghan forces.
The first ambush occurred along the Kabul-Kandahar highway, a ribbon of road that connects Afghanistan's two major cities. Long stretches of Highway 1 run through areas controlled by Taliban militants.
Six police were killed and five wounded in the ambush in southern Zabul province, said Gen. Yaqoob Khan, the provincial police chief. Two vehicles in the convoy were damaged, he said.
Taliban fighters also ambushed police in Logar province, killing six of the officers, said Gen. Mustafa Khan, the provincial police chief. The militants stole two police trucks in the clash in Kharwar district, he said. Most of the Taliban fled when NATO and Afghan reinforcements arrived on the scene, but eight fighters were captured, Khan said.
Afghan police are frequent targets of militant attacks, in part because the force has less training and is not as well equipped as the Afghan army.
In the east, insurgents attempted a double suicide bombing at Khost's provincial police station. One bomber blew himself up and killed at least three police. A second bomber who then ran into the police headquarters was shot and killed, said Mohammad Wali Shah, the police chief of Khost province.
In the southern Kandahar province, suspected Taliban militants ambushed two police officers riding a bike in Zhari district Tuesday, killing both, said Sayed Agha Saqib, the provincial police chief.
NATO-led and Afghan troops also clashed with Taliban in the same area, leaving four militants dead, Saqib said.
In Kabul, a suicide bomber on foot targeted a convoy of Turkish vehicles on the capital's outskirts, Turkey's Foreign Ministry and an Afghan police official said.
The attacker approached a car but could not open the locked door. He detonated the explosives on his body and the convoy then came under small-arms fire. Turkish guards responded with gunfire and one was wounded in the leg, Turkey's Foreign Ministry said in a statement.
The Taliban claimed responsibility for the attack, it said.
One Afghan was also wounded, said Zalmay Khan, Kabul's deputy police chief. Only the suicide bomber was killed.
In Paktia province, an attack on a road construction crew killed one person from the Philippines and wounded three guards, said Ghulam Dastager, the province's deputy police chief.
Elsewhere in Logar province, a government worker and his driver were assassinated in front of the worker's house, said Khan, the provincial police chief.
Violence has spiked in Afghanistan in the last several weeks. More than 3,300 people have died in insurgency-related violence this year, according to an Associated Press count based on numbers from Afghan and Western officials.
NATO's International Security Force said five advanced roadside bombs known as EFPs — explosively formed penetrators — have been found in Afghanistan this year. Two were found unexploded in Herat and two in Kabul. One detonated in the capital.
Col. Thomas Kelly, an ISAF official charged with countering homemade bombs, said the technology was likely brought in from outside the country.
Kelly said some of the EFPs may have been made in Iran, but that does not mean the Iranian government is behind their production.