US air strikes in the northern Afghan province of Kunduz killed about a dozen civilians on Saturday, local officials said, as battle intensified there and in southern Helmand province.

The air strikes killed 13 civilians, said Safiullah Amiri, a member of Kunduz provincial council. The casualties included children, said fellow council member Amruddin, who pegged the civilian death toll at 12.

The bodies were brought into Kunduz city in the back of a truck as part of protests by dozens of civilians against the deaths.

The civilian deaths occurred as Afghan and Taliban forces claimed to inflict heavy losses on each other in Kunduz and Helmand, two Taliban strongholds.

Sgt. Debra Richardson, spokeswoman for the Nato-led Resolute Support Mission in Afghanistan, said it is aware of the civilian casualty reports, adding that the mission reviews all credible allegations.

“We take every measure to prevent civilian casualties, in contrast to the Taliban who intentionally hide behind women and children,” she said in a statement.

Resolute Support, comprising troops from 39 countries, trains, advises and assists Afghan security forces.

Richardson said combined Afghan and US forces fought the Taliban for approximately 30 hours from Friday to Saturday near Kunduz city, during which Taliban manoeuvred in and out of civilian homes.

After killing 94 Taliban, some US and Afghan soldiers drove vehicles to a security checkpoint, where she said they were fired upon at close range. This was followed by Taliban fighters on either side of the checkpoint shooting at them.

An air strike was then conducted on a Taliban compound, one of a number that day, she said.

Four Afghan soldiers died in the fight, a senior Afghan military source said.

The Taliban said they had killed 19 members of Afghan forces and five from foreign forces in Kunduz. Kunduz is also where two US soldiers were killed in combat on Friday. The US Department of Defence identified the soldiers as Specialist Joseph Collette, 29, and Sgt. Will Lindsay, 33.

A record number of Afghan civilians were killed last year as aerial attacks and suicide bombings increased, the United Nations said in a February report.

Fighting has accelerated during a period of recurring peace talks. The latest negotiating round concluded this month with US and Taliban officials citing progress towards ending the 17-year war.

The Taliban have also caused civilian deaths in Helmand.

The militant group on Saturday claimed an attack at a stadium celebration of Farmers Day, which killed four people and wounded 31, including minor injuries to Helmand's governor.

A day earlier, Taliban attacked two Afghan outposts in Sangin, killing 48 Afghan security personnel, said Hashim Alokozay, a Helmand member of parliament. Taliban spokesman Qari Yousuf Ahmadi said the two outposts were over-run, killing 52 Afghan troops and wounding 11 more.

Omar Zwak, spokesman for Helmand's governor, said the Taliban also suffered heavy casualties.