Image copyright Reuters Image caption The gunmen attacked this guesthouse in the west of Kabul

Gunmen in the Afghan capital Kabul have attacked a guesthouse, killing a German woman and beheading an Afghan guard.

The attackers stormed a guesthouse run by a Swedish NGO, Operation Mercy, at about 23:30 (19:00 GMT) on Saturday, the Afghan interior ministry said.

A second woman, from Finland, is missing and has possibly been kidnapped, the ministry said.

In a separate attack, Taliban militants killed 20 police officers at checkpoints in southern Afghanistan.

At least 10 others were injured in the ambushes in Zabul province on Saturday, a provincial spokesman said.

Confirming the guesthouse attack, interior ministry spokesman Najib Danish said all those staying there were employees of Operation Mercy.

The relief and development organisation, based in Orebro in Sweden, has not yet commented.

Afghanistan is in the grip of an ongoing insurgency by the Taliban Islamist militant group, and several foreigners have been kidnapped by the group in recent years.

The British government warns there is "a very high and constant threat" to Westerners of kidnapping in Afghanistan, with about 100 people kidnapped since 2001.

But the threat of kidnap is far higher among Afghans, with the country's Chamber of Commerce and Industries reporting that at least 80 businessmen were snatched in 2016 alone.