Washington, Feb 27 (IANS): The US has offered rewards of up to $5 million for information on two associates of Afghan extremist group Hezb-e Islami Gulbuddin (HIG).

According to a US State Department statement Thursday, Secretary of State John Kerry has authorised a reward of up to $3 million for the arrest or conviction of Abdul Saboor and up to $2 million for Abdullah Nowbahar, Xinhua reported.

Saboor is an explosives expert associated with HIG who is responsible for an attack in Kabul May 16, 2013.

The attack killed two American soldiers, four US civilian contractors, and eight Afghans -- including two children-- and injured at least 37 others, the statement said.

Saboor and Nowbahar were key participants in an attack against a bus carrying foreign employees Sep 18, 2012.

More than a dozen people were killed and nearly a dozen more were injured in the attack.

HIG is an offshoot of Hezb-e Islami, or "Party of Islam", a political and paramilitary organisation in Afghanistan founded in 1976 by Afghan warlord Gulbuddin Hekmatyar.