President Vladimir Putin pledged Tuesday that Russia would maintain a $15 billion loan and cuts on energy prices to Ukraine even if the opposition came to power.

"In direct answer to your question as to whether we will review our agreements on loans and energy if the opposition comes to power - no we will not," Putin told a news conference at the close of talks in Brussels with the European Union's top officials.

Russia's top court on Thursday ordered the immediate release of oil tycoon Mikhail Khodorkovsky's jailed business partner, Platon Lebedev, whose term was due to end in May.

But the Supreme Court also effectively sealed the exile of Kremlin critic Khodorkovsky, who was released last month after receiving a pardon from President Vladimir Putin, by upholding the state's $550-million (400-million-euro) tax claim against him.

Russian President Vladimir Putin sat at a piano and picked out the melody of a popular Soviet-era song on Wednesday as a group of students sang along.

The strongman leader sat down at a grand piano at a top Moscow physics institute and played the song "Moscow Windows" while members of a male student choir joined in, the state RIA Novosti news agency reported.

Russia will not intervene in the raging anti-government protests in Ukraine and believes its leadership will find a way out, President Vladimir Putin's spokesman Dmitry Peskov said Thursday.

"We consider we do not have the right to intervene in any way in the internal affairs of our brother Ukraine. That's unacceptable and Russia has not done this and will not do it," Peskov said in an interview published on the website of Komsomolskaya Pravda daily.

Russian prosecutors on Wednesday demanded harsh jail sentences of five to six years for eight protesters on trial for a rally in 2012 ahead of Vladimir Putin's inauguration.

Several participants in the protest on Moscow's Bolotnaya Square on May 6, 2012, have been on trial since last June, accused of "mass riots" and hitting police after the rally turned violent.

Hungarian Prime Minister Viktor Orban meets Russian President Vladimir Putin on Tuesday for talks touching on a potentially huge contract for Russia to boost the EU nation's only nuclear power plant.

The Kremlin said in a statement that the two close trade and energy partners were holding "substantive discussions" on building up the capacity of Hungary's Paks facility.

Foreign Minister Mohammad Javad Zarif will head to Moscow Thursday for talks with Russian President Vladimir Putin on Iran's nuclear program and on regional issues including Syria, an official said.

"Zarif will meet the Russian president as well as Foreign Minister Sergei Lavrov during his one-day trip to Moscow on Thursday," Mehdi Sanaei, Iran's ambassador to Russia, told the official IRNA news agency.

Iranian President Hassan Rouhani said Thursday a Syrian peace conference planned for later this month will fail if Tehran, Damascus' main regional ally, does not participate, media reported.

The remarks came ahead of a meeting Monday at which Russia and the United States are to discuss Tehran's possible involvement in the talks set to start in Montreux, Switzerland on January 22.

Russian President Vladimir Putin and his Iranian counterpart Hassan Rouhani on Thursday discussed the Islamic republic's nuclear negotiations with world powers and Syria peace talks, the Kremlin said.

The leaders discussed "current international issues, including the situation in Syria in the context of preparations for the Geneva 2 conference, and the implementation of agreements on the Iranian nuclear program," the Kremlin said in a statement that did not specify who initiated the telephone call.

Former oil tycoon Mikhail Khodorkovsky, who was freed by Moscow last month after a decade in jail, vowed Sunday to fight for Russian political prisoners from his new base in Switzerland.

"You can't live with peace of mind when you know there are political detainees rotting in prison," Khodorkovsky told Swiss public television SRF on the train that took him from Berlin to Basel.