US blacklists Putin ally, alleged Litvinenko killers

The United States on Monday blacklisted five prominent Russians, including President Vladimir Putin's reputed top enforcer and the prime suspects in the murder of ex-spy Alexander Litvinenko in London a decade ago.

The US Treasury added Russia's senior federal investigator Alexander Bastrykin and alleged assassins Andrei Lugovoi and Dmitri Kovtun to the Magnitsky Act sanctions list.

Announcing the decision, the State Department did not detail what the new targets are accused of, but the move comes at a time of increased diplomatic tension with Moscow.

"Each of the most recently added names was considered after extensive research," spokesman John Kirby said, adding that the targeted names have "roles in the repressive machinery of Russia's law enforcement systems, as well as individuals involved in notorious human rights violations."

Under the act named after Russian tax fraud whistleblower Sergey Magnitsky, who died in a Moscow prison in 2009, people on the list have their US assets blocked and are banned from travelling to the US.

Asked why Obama's final update to the Magnitsky Act had still not included Putin himself, a senior administration official said Washington does not want a complete breakdown in ties.

The sanctions come amid worsening ties between the two countries. President Barack Obama's outgoing administration has accused the Kremlin of using cyber espionage, targeted leaks and propaganda in a bid to influence November's US presidential election.

US President-elect Donald Trump was angered when American intelligence agencies warned of the Russian hacking, alleging that they were behind a "witch hunt" to tarnish his win.

Moscow has scornfully rejected the charges, echoing US President-elect Donald Trump's "witch hunt" charge.

Trump is seeking to restore closer relations with Russia.