Afghan security forces have surrounded militants in Khost city, the capital of Khost province in east Afghanistan Monday and gun battle continues, police said.

"Three militants have been surrounded in a house and security forces are trying to arrest or kill them," a police officer at the site told Xinhua but he refused to be identified.

A militant hurled two hand grenades in Khost city in east Afghanistan Monday afternoon triggering gun battle. Minutes after throwing the hand grenades, another militant blew himself up.

However, police is reluctant to say if there were any casualties.

The attack and gun battle occurred hours after the visit of U.S. Defense Secretary Robert Gates to Afghanistan.

Gates arrived Monday morning to exchange views with President Hamid Karzai and NATO-led forces commander on the situation in Afghanistan.