By Maria Kiselyova and Ece Toksabay
MOSCOW/ISTANBUL (Reuters) - Six Russian warships are heading to the Black Sea from the Mediterranean for naval drills, the Interfax news agency cited Russia's Defence Ministry as saying on Tuesday, in what it said was a pre-planned movement of military resources.
Russia announced last month its navy would stage a sweeping set of exercises involving all its fleets in January and February, from the Pacific to the Atlantic, in the latest show of strength in a surge of military activity during a standoff with the West over Ukraine.
The six ships are scheduled to pass through Turkey's straits to the Black Sea on Tuesday and Wednesday, Turkish sources said.
The vessels include the Korolev, the Minsk and the Kaliningrad, which are set to navigate the Bosphorus on Tuesday, while the Pyotr Morgunov, the Georgy Pobedonosets and the Olenegorsky Gornyak are expected to pass on Wednesday.
Russia has amassed more than 100,000 troops near the Ukraine border. It denies any plans to invade but is seeking sweeping security guarantees, including a promise of no missile deployments near its borders, a scaling back of NATO military infrastructure and a ban on Ukraine ever joining the alliance.
Legally, NATO member Turkey could shut the straits to transit if Russia were to take military action against Ukraine.
"Turkey is authorised to close the straits to all foreign warships in wartime or when it is threatened by aggression. Also, it is authorised to refuse transit to merchant ships belonging to countries at war with Turkey," said Yoruk Isik, a geopolitical analyst based in Istanbul.
Turkey, which shares a maritime border with both Ukraine and Russia in the Black Sea, has said any military conflict would be unacceptable and has told Moscow any invasion would be unwise.
However President Tayyip Erdogan has also offered to mediate in the row between Moscow and Kyiv. Ankara has cordial relations with both countries, though Erdogan says it will do what is necessary as a NATO member in the event of a Russian invasion.
French President Emmanuel Macron said after talks in the Kremlin on Monday with Russia's Vladimir Putin that the coming days would be crucial in the standoff over Ukraine. Putin suggested some progress had been made in the talks.