Afghan officials said that one of the six officers to be killed by IS gunmen was a district police chief in the eastern Nangarhar province, where militant strikes have recently increased.

Attaullah Khogyani, spokesman for the provincial governor, said the insurgents attacked the administrative headquarters in Haska Mina district at 2 a.m. on Saturday.

The attack comes a day after three worshippers were killed and 70 wounded in a bomb attack on a mosque in the province.

"An attack deliberately targeting civilian members of a community praying together in a mosque can never be justified and highlights the perpetrators' intent to destroy lives, and spread terror among the civilian population," the UN said in a statement.

District police chief 'martyred'

"The district police chief Shah Mahmood was martyred along with five other policemen," Khogyani told news agency AFP.

"Eleven Daesh fighters were also killed and seven others were wounded," he added, using the Arabic acronym for the group.

IS fighters are making inroads into Afghanistan and challenging the Taliban in its own backyard in the country's east.

In March President Ashraf Ghani said the Islamists had been defeated, after local security forces claimed victory in a monthslong operation against the group.

But the group has also been intermittently airing propaganda through a mobile radio station, which the government claimed to have destroyed in an airstrike in February.

The Taliban, which is in a much stronger position than IS in Afghanistan, distanced itself from the attack.

US to focus on beating Taliban

Meanwhile, US officials said on Friday that President Barack Obama has ordered the US military to tackle the resurgent Taliban more directly - in tandem with Afghan allies.

US forces have been in an advisory role in Afghanistan since the start of 2015 and were only authorized to hit Taliban targets for defensive reasons, or to protect Afghan troops.

"This is using the forces we have ... in a better way, basically, as we go through this fighting season, rather than being simply reactive," Pentagon chief Ashton Carter said. "This makes good sense. It's a good use of the combat power that we have there."

Some 9,800 US troops remain in Afghanistan in an advisory capacity, down from a peak of around 100,000 in March 2011. That number is set to drop to just 5,500 by the year's end.

jbh/bk (AFP, AP)