The Obama administration has sanctioned Andrei Lugovoi and Dmitri Kovtun as alleged assassins of Alexander Litvinenko, a former Russian spy. The two are believed to be among the top allies of Russian President Vladimir Putin.

The two men allegedly poisoned Litvinenko in London in 2006.

The sanctioning took place under the Magnitsky Act, a United States law that allows punitive measures against Russians.

Lugovoi and Kovtun were among five Russians sanctioned under the Magnitsky Act.

Under the sanctions all their US assets freeze and they are bared from travelling to the country.

Federal prosecutor Alexander Bastrykin is one of Putin’s most powerful allies and is head of an investigative agency that had led alleged crackdowns on domestic dissidents.

Lugovoi and Kovtun were accused of poisoning Litvinenko, a former Russian agent turned freelance investigator who had collaborated with British intelligence.

Litvinenko is believed to have ingested polonium-210 , which is produced in nuclear reactors, while drinking tea with Kovtun and Lugovoi.

President Barack Obama’s outgoing administration has already accused the Kremlin of cyber espionage to influence the US elections and expelled 35 Russian diplomats over this case.

The Magnitsky Act was originally passed to enable US officials to impose sanctions on Russians implicated in the 2009 prison death of Russian tax fraud whistleblower Sergei Magnitsky.The total list of targets now includes 44 names.