Iraq voiced surprise Saturday after the US Treasury imposed "unacceptable" sanctions against Faleh Fayyadh, leader of the state-sponsored Hashed al-Shaabi, a powerful pro-Iranian paramilitary network.

Fayyadh is one of the most senior Iraqi state officials to be placed on the US sanctions blacklist.

Washington has been threatening for months to impose sanctions on Iraqis with close ties to Iran or accused of human rights violations, and the US Treasury said Fayyadh was responsible for brutal attacks on protesters in October 2019.

Fayyadh's former deputy, Abu Mahdi al-Muhandis, was killed in US drone strike a year ago alongside Iranian General Qassem Soleimani. 

But Iraq's foreign ministry called the blacklisting "surprising and unacceptable," and said it would "work to rectify" similar US moves against Iraqis, whether by outgoing President Donald Trump or his successor, Joe Biden.

The sanctions, announced Friday, seek to freeze any assets a designated person has under US jurisdiction and bans American firms -- including banks and other companies with US branches -- from doing business with them.

It poses a thorny problem for Fayyadh, a international businessman who has also been sent by Baghdad as an envoy to the US, Iran and the Gulf.

Iraqi national security adviser Qassem al-Araji said sanctions targeting a senior government official were an "error".

But several pro-Iran groups, including Lebanon's Hezbollah movement congratulated Fayyadh for the "honorary badge" of sanctions, saying it signalled his services to the "resistance".