WASHINGTON (Reuters) - The U.S. Treasury Department on Wednesday imposed new sanctions on five Russians and Chechens, including the head of the Russian republic of Chechnya, for alleged human rights abuses.

Head of the Chechen Republic Ramzan Kadyrov delivers a speech during a rally in support of Muslim Rohingya following the recent violence, which erupted in Myanmar, in the Chechen capital Grozny, Russia September 4, 2017. REUTERS/Said Tsarnayev

The new sanctions blacklisted Ramzan Kadyrov, the Chechen leader and a close ally of Russian President Vladimir Putin, the Treasury Department said in a statement.

U.S. authorities accused Kadyrov of overseeing “an administration involved in disappearances and extrajudicial killings”.

On a conference call with reporters Wednesday, a senior U.S. State Department official said that “one or more of Kadyrov’s political opponents were killed at his direction.”

Kadyrov reacted to news of the sanctions with his usual defiance.

“A sleepless night is waiting for me,” Kadyrov wrote, apparently sarcastically, on his Instagram social media account. “I can be proud that I’m out of favor with the special services of the USA. In fact, the USA cannot forgive me for dedicating my whole life to the fight against foreign terrorists among which there are bastards of America’s special services.”

He also wrote that he would not be visiting the United States.

The U.S. Treasury Department imposed the sanctions, which freeze the banks accounts of those targeted, under a 2012 law known as the Magnitsky Act.

The Magnitsky Act imposed visa bans and asset freezes on Russian officials linked to the death in prison of Sergei Magnitsky, a 37-year-old Russian auditor and whistleblower. The act also seeks to hold responsible those U.S. authorities allege orchestrated or benefited from the death of Magnitsky.

“Treasury remains committed to holding accountable those involved in the Sergei Magnitsky affair, including those with a role in the criminal conspiracy and fraud scheme that he uncovered,” Director of the Treasury Department’s Office of Foreign Assets Control John Smith said in a statement.

Magnitsky was arrested and died in a Moscow jail in 2009 after discovering a $230 million tax fraud scheme, according to U.S. authorities. Supporters of Magnitsky say the Russian state murdered him by denying him adequate medical care after he was imprisoned on tax evasion charges. The Kremlin denies the allegation.

In addition to Kadyrov and one other Chechen official, the Treasury’s action on Wednesday targeted three Russians that U.S. authorities say were involved in the complex tax fraud scheme that Magnitsky exposed.

The Magnitsky sanctions have been a point of tension between Moscow and Washington, even before Russia’s annexation of Crimea sent relations spiraling. In retaliation for the Magnitsky Act, Putin signed a bill halting U.S. adoptions of Russian children.

It had been unclear to sanctions experts whether President Donald Trump’s administration, which has signaled a desire to rebuild ties with Moscow, would continue to target people under the law.

The Magnitsky Act attracted greater public attention when it emerged that the president’s son Donald Trump Jr., had met with a Russian lawyer and a lobbyist - both strident opponents of the law - in New York ahead of the 2016 U.S. elections. When asked about the June 2016 meeting, Trump Jr. later said they discussed the adoptions issue.

On a conference call with reporters on Wednesday, State Department officials said that despite the new sanctions the Trump administration wants a constructive relationship with Moscow.

“We believe a Russia that takes care of the human rights of its own citizens will be an even more effective partner,” a senior State Department official said.