Russia fears new clashes in Ukraine's east

The Kremlin says it fears the resumption of full-scale fighting in eastern Ukraine and could take steps to protect civilians there, a stark warning that comes amid a Russian troop build-up along the border.

The statement by Russian President Vladimir Putin's spokesman, Dmitry Peskov, reflected the Kremlin's determination to prevent Ukraine from using force to try to reclaim control over separatist-controlled territory in the country's east.

Ukrainian forces and Russia-backed separatists have been fighting in eastern Ukraine since shortly after Russia's 2014 annexation of Ukraine's Crimea Peninsula.

More than 14,000 people have died in the conflict and efforts to negotiate a political settlement have stalled.

Ukraine and its allies have accused Russia of sending in troops and weapons to help separatists, accusations that officials in Moscow have denied.

Ukrainian President Volodymyr Zelenskiy visited his country's soldiers in the Donbas region on Thursday.

Ukrainian officials have raised concerns in recent weeks about increasingly frequent cease-fire violations in the country's industrial heartland known as Donbas.

They also expressed worries about the Russian troop build-up along the border with Ukraine.

During a call with Putin on Thursday, German Chancellor Angela Merkel "called for the removal of these troop reinforcements in order to achieve a de-escalation of the situation".

White House press secretary Jen Psaki said on Thursday that the US is also increasingly worried about the troop build-up, noting that Russia now has more troops on the border with Ukraine than at any time since 2014.

In response to those statements, Peskov said Russia is free to deploy its troops wherever it wants on its territory.

He accused the Ukrainian military of an "escalation of provocative actions" along the line of control in the east that threatens Russia's security.

"The Kremlin has fears that a civil war could resume in Ukraine and if a civil war, a full-scale military action resumes near our borders that would threaten the Russian Federation's security," Peskov said.

"The ongoing escalation of tensions is quite unprecedented."

Dmitry Kozak, a Putin aide who serves as Russia's top negotiator with Kyiv, warned Ukraine on Thursday against using force to retake control of the east, where many residents have Russian citizenship.

Such a move would mark "the beginning of an end for Ukraine," he said.

Kozak said Russia would likely act to protect civilians if they faced a potential massacre like the one that took place during the Bosnian war in Srebrenica in 1995.

Asked about Kozak's comment, Peskov said that in the case of a Srebrenica-like threat, "all countries, including Russia, will take steps to prevent such tragedies".

He alleged that virulent nationalist rhetoric in Ukraine was inflaming hatred against the mostly Russian-speaking population of the east.

A Turkish Foreign Ministry official said on Friday that the United States has notified Turkey that two US warships will sail to the Black Sea on April 14 and April 15 and stay there until May 4 and May 5 respectively.

The official, speaking on condition of anonymity in line with government rules said the US notified Turkey 15 days prior to the ships' passage in line with a convention regulating shipping through the Turkish straits.