Eighteen people, including eight children, have been killed in two separate suicide bomb attacks in Afghanistan.

Nine civilians were killed in an explosion at a defence ministry gate in the capital, Kabul.

Another suicide attack killed eight children and a policeman in Khost in the south east of the country. 

The incident in Kabul happened during a visit by US Defense Secretary Chuck Hagel.

Mr Hagel was nowhere near the explosion according to a spokesman for Afghanistan's NATO-led International Security Assistance Force.

Fourteen people were wounded in the attack, carried out by an insurgent on a bicycle.

Roads around the ministry building, which is near the presidential palace, were closed as emergency officials cleared the area of debris and washed blood from the street.

A wall surrounding the ministry was pockmarked with shrapnel.

The Afghan Taliban claimed responsibility for the attack and said the ministry was the target.

They said in a statement the attack "is a kind of message" for Mr Hagel.

The blast underscored the security challenges facing Afghanistan as US-led NATO forces prepare to leave the country by the end of 2014.

Some Afghans fear that another civil war could erupt or the Taliban will make a push to take control of the country again after Western combat troops withdraw.

Mr Hagel arrived in Afghanistan for his first trip abroad as defense secretary and was moved from a briefing room at a NATO base to a more secure location after the blast.

The explosion was audible during a briefing for reporters travelling with Mr Hagel.

After the blast, he flew to Bagram Air Base near Kabul for closed-door meetings with commanders.

Mr Hagel is due to hold talks with President Hamid Karzai, whose recent orders to curtail US military activity highlights an often tense relationship with the 66,000 American forces.