Moscow – The Kremlin is indignant over the comments of a Fox News host who called Russian President Vladimir Putin a "killer" in an interview with President Donald Trump.In the interview broadcast over the weekend, Bill O'Reilly called the Russian leader "a killer". Trump replied that the US has killers, too.Putin's spokesperson Dmitry Peskov refused to comment on Monday on Trump's reply, but lashed out at Fox News, calling O'Reilly's remarks "unacceptable and offensive"."We would like to receive an apology from the president from this respected organisation," Peskov told reporters on Monday, referring to Fox News."I'm working on that apology," O'Reilly told viewers on his Fox News programme on Monday night, "but it may take a little time. You might want to check in with me around 2023."Multiple killingsA British judge concluded last year that two Russians, acting at the behest of Moscow's security services and probably with approval from Putin, poisoned ex-KGB agent Alexander Litvinenko at a London hotel in 2006.Litvinenko died after drinking tea spiked with a fatal dose of radioactive polonium-210. The Kremlin angrily dismissed the inquiry as a "quasi-investigation".Putin's critics in Russia and abroad also held him politically responsible for the 2006 killing of investigative journalist Anna Politkovskaya and the 2015 slaying of leading Kremlin critic Boris Nemtsov. The critics said the atmosphere of intolerance to dissent under his watch contributed to the two killings.In 2014, a court in Moscow convicted the gunman and three other Chechens involved in Politkovskaya's killing along with a former Moscow policeman who was their accomplice. Investigators have failed to track down the mastermind.Five suspects, all of them Chechens, went on trial in the fall for their alleged roles in Nemtsov's murder. The suspected triggerman served as an officer in the security forces of the Moscow-backed Chechen regional leader, Ramzan Kadyrov.Trump has praised Putin and signalled that US-Russia relations could be in for a makeover under his leadership. Putin in his turn spoke warmly of Trump.