Russian Foreign Minister Sergei Lavrov said Monday crimes committed against Christians in the Middle East were tantamount to "genocide", joining other high-ranking diplomats in calling for action.

Like other minorities, Christians have been the target of brutal violence waged by jihadists in countries such as Libya or Syria.

Poland's Senate speaker Bogdan Borusewicz said Monday that Russia had denied him entry for the funeral of outspoken opposition activist Boris Nemtsov, who was gunned down in central Moscow on Friday.

"I wanted to pay respect to the slain Boris Nemtsov and to all Russians who think like him. But I have just learned Russian authorities will not allow me to attend the funeral in Moscow," said Borusewicz, a key communist-era dissident and founding member of Poland's anti-regime Solidarity movement.

France will "not tolerate the slightest infringement" of the Minsk peace accord in Ukraine warned President Francois Hollande following a meeting with NATO chief Jens Stoltenberg in Paris Monday.

"The Minsk accord is the only possible basis to re-establish peace," Hollande told reporters.

Estonia's governing pro-NATO Reform party was set Monday for tricky coalition talks after defeating a Kremlin-oriented rival in an election held amid jitters over the actions of neighboring Russia.

President Toomas Hendrik Ilves is expected to task Reform leader and outgoing Prime Minister Taavi Roivas with forming a government after the centrist party won 30 seats in the 101-member parliament in Sunday's vote.

Russia vowed Monday to find the killers of outspoken opposition leader Boris Nemtsov as fresh details emerged about the most shocking political assassination during Vladimir Putin's rule.

The 55-year-old former deputy prime minister, a longtime Putin critic and renowned anti-corruption crusader, was shot dead shortly before midnight Friday while walking across a bridge just a short distance from the Kremlin.

The EU said it hoped for a "positive outcome" in talks in Brussels on Monday between the Russian and Ukrainian energy ministers aimed at resolving a gas supply dispute threatening deliveries to Europe.

Russian state-owned gas giant Gazprom threatened last week to cut deliveries to Ukraine and divert supplies instead to eastern parts of the country controlled by pro-Kremlin rebels.

The U.S. and Russian foreign ministers expressed cautious optimism after holding talks in Geneva Monday to end fighting in Ukraine, where the U.N. says more than 6,000 people have died in less than a year.

The meeting between John Kerry and Sergei Lavrov in Geneva was just one of several attempts at mediation on the conflict Monday, as high-stakes talks to resolve a bitter gas dispute between Kiev and Moscow took place in Brussels.

U.N. rights leaders on Monday decried the "merciless devastation of civilian lives and infrastructure" in Ukraine as the death toll passed 6,000, warning that targeting civilian areas could be a "crime against humanity."

The United Nations' ninth report on the situation in violence-wracked Ukraine paints a bleak picture of developments in the country and warns there has been a "serious escalation" of the conflict since the beginning of the year.

Estonia's security-minded center-left governing coalition took the lead in Sunday elections, held amid concerns over a militarily resurgent Russia, while the pro-Kremlin opposition lost ground, partial official results showed.

The ruling coalition was leading in 51 of the 101 parliamentary seats with over half of the votes counted.

A Ukrainian lawmaker said Sunday he was detained by Russian police ahead of a Moscow march to honor opposition leader Boris Nemtsov, who was gunned down near the Kremlin.

"Police have detained me," Alexei Goncharenko wrote on Facebook. "I did not shout anything, did not carry any banners or flags -- they simply detained me over the T-shirt."