Russia's military on Tuesday said its planes did not carry out any strikes near the town of Khan Sheikhun in Syria, where air strikes hit a hospital as doctors treated victims of a suspected chemical attack.

The Kremlin on Tuesday called the Saint Petersburg metro attack that left 14 dead and injured dozens a "challenge" to all Russians, including President Vladimir Putin.

Anti-corruption campaigner Alexei Navalny has cemented his status as leader of Russia's opposition movement by organizing the largest unauthorized protest in recent years against President Vladimir Putin's rule.

A Russian court on Monday sentenced Kremlin critic Alexei Navalny to 15 days behind bars after ruling he had resisted police during an anti-corruption protest Sunday in Moscow.

Russia's central bank cut its key rate Friday for the first time in six months and said more cuts were coming, offering a welcome boost to the country's struggling economy.

It was the year that ended centuries of royal rule, brought two revolutions, ushered in Soviet domination and changed the course of Russian history irrevocably.

Four Russian military personnel were killed and two injured when their vehicle was targeted with explosives in central Syria last week, a defense ministry statement quoted by Russian agencies said Monday.

President Vladimir Putin on Thursday called for Russian intelligence agencies to bolster ties with their US counterparts in the fight against terrorism.

"Restoring dialogue with the special services of the United States and other NATO members is in our mutual interest," Putin told the country's FSB intelligence agency in a televised speech. 

President Donald Trump on Wednesday dismissed talk of a Russian connection as "non-sense," two days after the resignation of his national security adviser Michael Flynn renewed questions about Moscow interference in U.S. politics.

"This Russian connection non-sense is merely an attempt to cover-up the many mistakes made in Hillary Clinton's losing campaign," Trump said in an early morning post on Twitter.

Russia and Turkey on Wednesday staged their first joint air strikes against the Islamic State jihadist group in Syria, the Russian defense ministry said.