A suicide bomber on a motorbike detonated his explosives near a busy bazaar in Afghanistan's northern Parwan province on Tuesday morning, killing at least six people, officials said.

Earlier, a gunbattle with the Taliban in southern Uruzgan province late on Monday night left at least 12 security forces killed, according to Raheemullah Khan, the province's deputy police chief.

Mohammad Sayed Seddiqi, administrative chief of Siagird district, said the motorbike bomber struck during the traditionally busy morning hours, targeting the local police headquarters. No policemen were among the six killed, but at least one officer was among the 26 wounded, he added.

Guards had spotted the bomber and ordered him to stop before he was able to enter the police compound and cause more casualties, said district police commander, Haroon Mubarez.

No one immediately claimed responsibility for the Parwan attack.

In the Uruzgan assault, "the battle began when Afghan security forces tried to take control of the highway between Dihrawud and the provincial capital, Tarin Kot, from the Taliban," said Khan.

The highway has been contested between Afghan government forces and the Taliban for about 25 days, he said, and the fighting for control of a section of the highway has caused high casualties on both sides.

The Taliban have stepped up their attacks on Afghan security forces over the past year as they intensify their 15-year war to overthrow the Kabul government.

About 5,500 Afghan security forces personnel were killed in action in 2015, U.S. Army Gen. Charles Cleveland, spokesman for the U.S.-NATO mission in Afghanistan, said on Tuesday.

The figure is about 30-percent higher than the previous year, when international combat troops were leading the fight against the insurgents. Most international troops left the country at the end of 2014, leaving behind around 13,000 U.S. and NATO soldiers operating in a mostly supportive role.

A small contingent of Americans are involved in a counter-insurgency mission mandated to seek out Taliban, al-Qaida and Islamic State group fighters.

Cleveland said  U.S. forces had conducted just under 100 counter-terrorism "kinetic strikes" between Jan. 1 and March 31 this year, mostly in Nangarhar province, bordering Pakistan, against IS and "some against al-Qaida."

He estimated that the strikes had reduced the number of IS operatives in Afghanistan to around 1,000, from earlier estimates up to 3,000.