Russian state news agency TASS said on Friday that the authorities were raiding its Moscow headquarters in relation to an employee's former occupation.

"The searches that are being conducted are linked to a TASS employee," agency spokeswoman Yekaterina Titova told AFP.

Russia on Thursday accused Turkey of actively preparing to invade Syria, saying it had spotted troops and military equipment on the border with the war-torn country.

"We have serious grounds to suspect Turkey is in intensive preparations for an armed invasion of the territory of a sovereign state -- the Syrian Arab Republic," the defense ministry said in a statement.

Russia urged North Korea on Thursday to avoid escalating tensions with a planned rocket launch, expressing "grave concern" over the announcement.

The Russian foreign ministry said in a statement that it had summoned the North Korean ambassador in Moscow over Pyongyang's announcement that it will launch a satellite-bearing rocket sometime between February 8-25.

U.S. Secretary of State John Kerry demanded Thursday that Russia stop bombing the Syrian opposition, implicitly blaming Moscow for the collapse in peace talks.

Speaking in London ahead of a conference on the Syrian humanitarian effort, Kerry said he had called Russian Foreign Minister Sergei Lavrov for a "robust" discussion.

Turkey on Thursday said that it had refused to allow a Russian reconnaissance plane to overfly its territory near Syria, citing a disagreement over the flight plan, as relations between the two countries hit a post-Cold War low.

The Turkish foreign ministry's statement came a day after Russia accused Turkey of breaching the Open Skies treaty by refusing the plane access.

A Russian opposition party on Wednesday demanded a formal investigation into Chechen strongman Ramzan Kadyrov after he posted a video of its leader in the cross hairs of a sniper scope.

A video posted Monday on Kadyrov's popular Instagram page showed former prime minister Mikhail Kasyanov, the Parnas party leader, along with his deputy targeted in the sights of a sniper rifle.

Russia said Wednesday it would press ahead with its bombing campaign in Syria until "terrorist organizations" such as the Islamic State group are defeated amid the latest international push to end the conflict.

"Russian air strikes will not cease until we truly defeat the terrorist organizations ISIL and Jabhat al-Nusra," Russian Foreign Minister Sergei Lavrov told reporters in Oman, referring to the IS and Al-Nusra Front jihadist groups, Interfax news agency reported.

Turkey on Saturday accused Russia of a new violation of its airspace, warning Moscow against "irresponsible behavior".

"A Su-34 plane belonging to the Russian Federation air force violated Turkish airspace at 11:46 (0946 GMT) local time yesterday (Friday)," the foreign ministry said in a statement.

A powerful 7.0-magnitude earthquake struck in Russia's Far East on Saturday morning, U.S. and Russian authorities said, although there were no reports of any casualties.

The U.S. Geological Survey said the quake occurred at 0325 GMT at a depth of 160 kilometers (100 miles), in the mountainous Kamchatka Krai region on Russia's eastern coast.

A Turkish citizen fighting in Syria who Moscow has accused of killing a Russian pilot said Friday he was not scared Russian forces are targeting him, after making an unexpected public appearance in Istanbul.

Alparslan Celik has been accused by Russia of killing in cold blood Russian pilot Oleg Peshkov as he parachuted to the ground after his plane was shot down by Turkish air forces on the Syrian border on November 24.