The marginalized Russian opposition parties of slain Kremlin critic Boris Nemtsov and arch Putin foe Alexei Navalny have announced they will form an alliance for legislative polls in 2016.

Nemtsov's RPR-Parnas and Navalny's Party of Progress said Friday they are joining forces to put forward joint candidates at local elections this year and parliamentary polls next year.

French President Francois Hollande will discuss the Ukraine crisis with his Russian counterpart Vladimir Putin during a visit to Armenia on April 24, a source in his office said Friday.

Putin and Hollande are attending a ceremony in Yerevan marking the 100th anniversary of the Armenian genocide.

Russian President Vladimir Putin on Thursday admitted that the Soviet Union had sought to forcibly impose the Soviet model on Eastern Europe after World War II.

"After WWII we tried to impose our model of development on many Eastern European countries and did it by force," Putin said during his annual phone-in with Russians.

Armed police on Thursday raided the office of a Russian rights group led by the exiled critic of Vladimir Putin, Mikhail Khodorkovsky, during the president's marathon annual phone-in session.

A group of police and special forces came to the Moscow office of Open Russia, a rights network led by Khodorkovsky, and searched the premises for protest fliers, Khodorkovsky's spokeswoman Kulle Pispanen wrote on her Facebook page.

President Vladimir Putin on Thursday said the worst was over for Russia's crisis-hit economy, pointing to the recent rebound of the ruble despite Western sanctions over Ukraine.

"The ruble has stabilized and strengthened," Putin said during his annual phone-in with Russians. "Experts believe that we have passed the peak of the problems."

Poland's prime minister on Wednesday criticized a fiercely nationalistic Russian biker gang's plans to ride through Europe to celebrate the Soviet Union's victory over Nazi Germany in World War II. 

The two-week 6,000-kilometer (3,750-mile) rally by Russian bikers including the Night Wolves, a motorcycle club backed by Russian President Vladimir Putin, comes as tensions run high between Russia and the West over the crisis in Ukraine.

President Vladimir Putin on Monday opened the way for Russia's delivery of a sophisticated air defense missile system to Iran, a move that would significantly bolster the Islamic republic's military capability.

U.S. Secretary of State John Kerry objected to Moscow's decision in a phone call to Russian Foreign Minister Sergey Lavrov, and the White House indicated the move could endanger plans to ultimately lift sanctions on Iran as part of a final nuclear deal.

Latvia, current holder of the EU presidency, said Friday it was surprised by Greek Prime Minister Alexis Tsipras' criticism of European Union sanctions against Russia.

The Latvian prime minister's comments came after left-wing Tsipras met with Russian President Vladimir Putin on Wednesday, and lashed out against what he termed the EU's "vicious cycle of sanctions."

Russian President Vladimir Putin will meet Palestinian leader Mahmoud Abbas in Moscow on Monday where the issue of Middle East peace talks will be raised, Russian authorities announced Thursday.

"The two leaders will hold talks concerning key aspects of Russian-Palestinian relations and their future, with particular attention on the trade, economy and humanitarian sectors," the Kremlin said in a statement.

Spain on Thursday defended EU sanctions on Russia over Ukraine, rejecting repeated criticism of the measures by Greek Prime Minister Alexis Tsipras.

During a joint news conference with Russian President Vladimir Putin in Moscow on Wednesday, Tsipras said the European Union needed "to leave behind this vicious cycle of sanctions".