German Foreign Minister Frank-Walter Steinmeier on Tuesday warned all sides in the Ukraine conflict against acts of "sabotage", speaking on the eve of a planned Ukraine peace summit in Minsk.

"It wouldn't be the first time that an act of political sabotage, a targeted strike, destroys all hopes of a ceasefire," he said.

Kiev has requested a restructuring of its debt to Russia but Moscow is expecting its $3 billion loan to be repaid in full this year, Russia's finance minister said Tuesday.

"Ukraine asked us to review the issue of restructuring its debt," Finance Minister Anton Siluanov told Russian media on the sidelines of the G20 summit of finance ministers and central bank chiefs in Istanbul.

Ukraine on Tuesday replaced its chief prosecutor, criticized over the stalled probe into the killing of more than 100 demonstrators during protests in Kiev last February. 

Lawmakers voted to dismiss Vitaliy Yarema after failing to prosecute anyone from the regime of former president Viktor Yanukovych for the fatal shooting of protesters on Kiev's iconic Independence Square.

French President Francois Hollande said Tuesday he was going to Minsk with the "strong will" to achieve a peace deal on Ukraine at a four-way summit also attended by German Chancellor Angela Merkel.

The Russian and Ukrainian leaders were also due to be present at the meeting in the Belarusian capital Wednesday, as fighting rages on in the east of Ukraine.

Britain reserves the right to arm Ukraine and will not allow the Ukrainian army to collapse, Foreign Secretary Philip Hammond told parliament on Tuesday.

"It's a national decision for each country in the NATO alliance to decide whether to supply lethal aid to Ukraine," he said in a statement to MPs.

U.S. President Barack Obama on Monday agreed to hold off a controversial decision on sending arms to Ukraine until German-led efforts to broker a ceasefire with Russia are given a chance. 

Hosting Chancellor Angela Merkel at the White House, Obama said he hoped she could reach a deal with Russian President Vladimir Putin to end 10 months of bloodshed in eastern Ukraine, but warned more punitive measures are in the pipeline if that fails.

U.S. President Barack Obama said Monday no decision had been made on whether to send weapons to Ukraine to help Kiev battle pro-Russian separatists, as he warned the West would not allow Russia to redraw Europe's borders by force.

Obama, who has faced increasing calls from domestic critics to supply the outmatched Ukrainian army with more weapons to shore up its faltering defenses, said he was still mulling his options.

Russia has accused a former employee of the Moscow Patriarchate of state treason, the latest person suspected of committing a grave crime against the state amid tensions with the West over Ukraine.

Yevgeny Petrin, who had worked for the Moscow Patriarchate in Ukraine, was detained on charges of treason last June, a spokeswoman for Moscow's Lefortovo district court told Agence France-Presse on Monday. 

Anti-Western sentiment has reached historic levels in post-Soviet Russia, with a vast majority expressing negative attitudes towards the United States and the European Union, a poll showed on Monday.

Relations with the United States, the former Cold War era rival, have never been particularly warm under Vladimir Putin, but ties appear to have come undone since the start of the Ukraine crisis more than a year ago, a study by the respected Levada Center pollster showed.

The EU has agreed to postpone new sanctions against Russia to give time to see if a four-way Ukraine peace summit Wednesday makes progress, French Foreign Minister Laurent Fabius said.

"The principle of the sanctions will be kept, but their implementation will depend on the situation on the ground," Fabius told reporters in Brussels. "We will assess the situation again next Monday."