Britain's treasury chief, Gordon Brown, has ordered a freeze on any British assets of a militant group that claimed responsibility for kidnapping and beheading two Americans and one Briton in Iraq in the past month.

Thursday's announcement said the order freezing the assets of the Tawhid and Jihad group takes effect immediately.

It is unclear whether the group has any assets in British accounts.

The group is headed by Jordanian-born Abu Musab al-Zarqawi, considered the most wanted man on the list of terrorist suspects being hunted in Iraq.

The United States has offered a $25 million reward for his capture.

In addition to kidnapping and killing hostages, the Zarqawi group has organized suicide bombings and the assassinations of Iraqi officials.