At least 13 dead in Afghan city bombing

At least two children were among the wounded, the information ministry said.

The attacker targeted police vehicles in the centre of Khost. So far no group has claimed responsibility although the Taliban and the group known as Islamic State will be the main suspects.

There has been a surge in violence in several parts of Afghanistan recently - much of it involving the Taliban.

On Friday at least 15 soldiers were killed in a Taliban attack on a military base in Kandahar province.

Saturday's bombing took place as the country marked the first day of Ramadan, a month of prayer and fasting for Muslims.

It was detonated near a military base, officials say.

A public bus station bore most of the force of the blast which targeted Afghan security forces working with American troops in Khost province, ministry spokesman Najib Danish told the AFP news agency.

"The bodies are not recognisable and it is hard to say if they are civilians or security forces," he added.

The latest violence is a challenge for Nato-backed Afghan forces and raises further concerns about their ability to see off the militant threat.

Both the military and security forces have sustained unprecedented casualties recently in addition to a high level of desertions and numerous corruption scandals.

The Taliban began their yearly spring offensive at the end of last month and soon afterwards the US said it was considering the deployment of at least 3,000 more troops to bring a measure of stability to the country.

Last month, the Taliban killed at least 135 Afghan soldiers in a military compound near the northern city of Mazar-e Sharif.

US combat operations against the Taliban officially ended in 2014, but special forces have continued to provide support to Afghan troops.

The Taliban is believed to control up to a third of Afghanistan, after gaining ground in the past two years.