The United States has offered $20m for information on four senior members of the Islamic State of Iraq and the Levant (ISIL) group, the State Department has said.

A statement released on Tuesday said that the US Secretary of State John Kerry had authorised payments for intelligence on Abd al-Rahman Mustafa al-Qaduli, Abu Mohammed al-Adnani, Tarkhan Tayumurazovich Batirashvili and Tariq Bin-al-Tahar Bin al Falih al-'Awni al-Harzi.

Kerry offered a $5m reward each for information on Adnani, the group's spokesman, and Batirashvili, also know as Omar al-Shishani, the group's military commander.

Qaduli, a senior leader of the group, and an early follower of the founder of the group, Abu Musab al-Zarqawi, attracted a $7m award for information on his whereabouts. He served as the group's chief in Mosul during the US occupation of Iraq, when the group went by the name al-Qaeda in Iraq.

The US is also offering $3m for information on Harzi, a Tunisian national, who has been accused of being a financier for the group, which has conducted dozens of bomb attacks and mass killings in Iraq and Syria.

The US has already offered a $10m reward for information about the group's leader, and self-proclaimed caliph, Abu Bakr al-Baghdadi.

ISIL captured huge swaths of territory in Iraq and Syria during a campaign in 2014, bringing it into conflict against the Syrian and Iraqi government, as well as Syrian rebel factions.

The group's advances in Iraq led to a US-led coalition air campaign against ISIL positions in both Iraq and Syria.

The group has abducted and executed a number of US hostages, including US journalists James Foley and Steven Sotloff, and aid worker Abdul Rahman (Peter) Kassig.