The US on Wednesday designated a powerful Iraqi paramilitary leader as a terrorist after rocket attacks, and vowed to step up pressure on his ally Iran.
The State Department listed Ahmad Al Hamidawi, secretary general of the armed faction Kataib Hezbollah, as a "specially designated global terrorist", freezing any US assets he may hold and making American transactions with him a crime.
Al Hamidawi took over the leadership from Abu Mahdi Al Muhandis, who was killed in a US drone attack in Baghdad on January 3.
Al Muhandis died alongside top Iranian general Qassem Suleimani, leader of the Islamic Republican Guard Corps' Quds Force.
The group, which has a close relationship with Iran, has been designated as a terrorist group by the US since 2009.
"Today we are intensifying our pressure on this terrorist group," said Nathan Sales, the State Department counter-terrorism chief.
Mr Sales said that the group's goal was to "advance the Iranian regime goal of turning Iraq into a vassal state".
The State Department said Kataib Hezbollah's rocket attacks included one on December 27 against an Iraqi base that houses US troops, in which an American contractor was killed.
The incident sent tension soaring, with the US bombing paramilitary targets and eventually killing Suleimani and Al Muhandis at Baghdad airport.
The State Department also pointed to indications that Kataib Hezbollah was behind deadly sniper attacks against demonstrators in October in Baghdad.
National protests, sparked by economic concerns, brought down a government with close ties to Iran.
Secretary of State Mike Pompeo on Sunday spoke by phone to Iraq's designated Prime Minister, Mohammad Allawi, and urged the government to protect US forces.
