The Pakistani Taliban has claimed responsibility for the deadly suicide bombing inside the U.N. World Food Program headquarters in Islamabad.

Taliban spokesman Azam Tariq said Tuesday his group was behind Monday’s blast, which killed five U.N. employees and wounded five others. 

He said the Taliban believes international organizations such as the World Food Program promote what he called a “U.S. agenda” in the country.

Pakistan’s Interior Ministry says Taliban militants were retaliating for military operations in Swat and South Waziristan. 

Interior Minster Rehman Malik said Monday the bomber, wearing a security guard uniform, detonated about eight kilograms of explosives in the lobby of the U.N. aid agency.  The minister warned people to prepare for more attacks in the coming days.

WFP officials said four Pakistanis and one Iraqi national were killed.

The United States condemned the bombing.

State Department spokesman Ian Kelly said such “senseless acts of violence against people who help feed the poor and hungry are an attack on civilization itself, and expose the true nature of the terrorist agenda.”

U.N. officials denounced the attack.  They said they had closed all offices in Islamabad and neighboring Rawalpindi until further notice, but that the operations are ongoing. 

The WFP is active across the country and recently provided food aid to civilians displaced by fighting in the Swat Valley region.

Some information for this report was provided by AFP and AP.