Ukraine must pay for Russian gas being supplied to rebel areas in the country's war-torn east, Russian Prime Minister Dmitry Medvedev said Friday, raising the possibility of another gas dispute in the midst of winter.

Russian gas giant Gazprom began direct deliveries to separatist areas on Thursday in addition to other areas of Ukraine after Kiev temporarily cut supplies.

A stream of sombre Ukrainians on Friday laid flowers at memorials on Kiev's Independence Square where one year ago scores of demonstrators were gunned down in the final act of a dramatic uprising. 

Some wept and others crossed themselves in silence in front of the pictures of some 100 protesters who died during the months of protests that eventually toppled Kremlin-backed president Viktor Yanukovych.

Australia on Friday said France, Germany and Japan were potential partners to design and build its next generation of submarines, in what will be its biggest ever defense procurement program.

As Canberra seeks to replace its ageing Collins Class fleet, Defense Minister Kevin Andrews said all three countries had proven military design and build capabilities and were currently producing submarines.

A Russian court has jailed top Kremlin critic Alexei Navalny for two weeks in a move that prevents the charismatic leader from attending a massive opposition protest planned for March 1.

The Moscow Presnensky court ruled that Navalny, who has a string of probes against him and was given a suspended prison sentence in December, organised an illegal gathering in the capital's subway by handing out flyers advertising the March 1 protest.

The United States voiced fears Thursday that the Palestinian Authority may be teetering on the brink of collapse because of a lack of funding, as Israel withholds taxes and donor aid stalls.

Washington has been in urgent talks with regional leaders as well as other stakeholders in the frozen Middle East peace process in a bid to try to release more funds.

Britain and Spain said Thursday the solution to the Ukrainian conflict had to come through dialogue and should not involve military aid to Ukrainian forces.

"We do not believe that at the moment it would be helpful to provide lethal support to the Ukrainian armed forces," British Foreign Secretary Philip Hammond told a news conference with Spanish Foreign Minister Jose Manuel Garcia Margallo in Madrid.

Russia's Gazprom on Thursday started supplying gas directly to the rebel-controlled area in east Ukraine after pro-Moscow separatist leaders said Kiev had cut supplies, the company's chief said.

"From 1600 (1300 GMT) on February 19, Gazprom is supplying gas to Ukraine including through the Prokhorovka and Platovo gas metering stations to an amount of 12 million cubic meters per 24 hours," said Alexei Miller, quoted by RIA Novosti news agency.

The leaders of Ukraine, Germany, France and Russia on Thursday pledged to try to save a tattered ceasefire in eastern Ukraine despite violations -- including the storming of a key town by pro-Russian rebels.

As the leaders condemned the fighting and urged both sides to observe the truce, there was strident opposition from the separatists and Moscow to a plea from Ukraine for international peacekeepers to enforce the ceasefire.

Russia could inflict the tactics it is accused of using to destabilize Ukraine on Baltic members of NATO, Britain's defense minister warned in comments to British newspapers on Wednesday.

Michael Fallon said that NATO must be prepared for Russian aggression in any form, and warned of a "real and present danger" to Baltic members of NATO -- eurozone members Estonia, Latvia and Lithuania.

Despite strained U.S.-Russian ties, the head of Russia's FSB security forces was Wednesday leading Moscow's delegation to a White House summit aimed at battling violent extremists, a U.S. official said.

Alexander Bortnikov, who heads the powerful intelligence agency, is one of the highest level Russian officials to visit Washington in recent months as tensions have flared over the conflict in eastern Ukraine.