Secretary of State Mike Pompeo on Saturday said Washington pledged "up to $1 billion" to boost energy projects in eastern Europe as part of efforts to reduce reliance on Russian natural gas.

Russian President Vladimir Putin and Turkish leader Recep Tayyip Erdogan have discussed de-escalation of the Syrian crisis, the Kremlin said Wednesday, adding that Russian-Turkish agreements should be implemented in full.

Turkey warned Russia not to get involved as it retaliated against Syrian government forces for killing four of its soldiers in northwest Syria on Monday.

Russian lawmakers on Thursday unanimously approved a sweeping constitutional reform bill put forward by President Vladimir Putin in its first reading, after less than two hours of debate.

Russian lawmakers will begin reviewing President Vladimir Putin's nomination of a little-known tax chief as the new prime minister Thursday after his announcement of a sweeping constitutional shake-up fuelled speculation about his future plans.

Russian Defence Minister Sergei Shoigu told President Vladimir Putin on Friday that the country's first Avangard hypersonic missiles have been put into service, an official statement said.

"The first missile regiment equipped with latest strategic missiles with the Avangard hypersonic glide vehicle entered service at 10 am Moscow time on December 27", the defence ministry said, according to Russian news agencies.

Russia expects to complete construction of the major Nord Stream 2 pipeline under the Baltic Sea despite approval by the US Senate of sanctions against companies working on the project, the Kremlin said Wednesday.

Russian leader Vladimir Putin is set Saturday to address a United Russia convention as the ruling party struggles to overcome a crisis amid the public's growing desire for change.

Russia said Monday it had handed over three navy ships it seized a year ago from Ukraine, in the latest move to ease tensions between the two countries ahead of a crucial summit.

President Vladimir Putin hosts dozens of African leaders next week as Russia seeks to reassert its influence on the continent and beyond.