"One Afghan and one foreigner, both working for a foreign organisation, were killed," Hashmat Stanakzai, spokesman for the Kabul police, told AFP.
He declined to identify the nationality of the foreigner or the targeted organisation.
"Three suicide bombers targeted this building," he said. "The Afghan security forces quickly reached the site of the attack, and started operations against them.
"Fighting was over after three hours, with all three militants killed. Six people were rescued."
"A spate of deadly martyrdom attacks have rocked important enemy targets in recent days," Mujahid added.
Kabul has been hit by at least nine attacks in the last two weeks, with targets including US military convoys, security contractor compounds and a female Afghan member of parliament.