Ukrainian President Petro Poroshenko has ordered a “quick and transparent” investigation has been ordered into the murders of a pro-Russian journalist and a former politician loyal to the ousted former leader Viktor Yanukovich.
Oles Buzina, 45, was known for his pro-Russian opinion pieces published in Ukraine's Sevodnya daily newspaper, and was shot dead by two masked gunmen in Kiev.
Ex-member of parliament for Yanukovich's discredited Party of Regions, Oleh Kalashnikov, was killed in a similar attack as he entered his home the day before.
In an official statement, President Poroshenko said; “Their nature and political import are clear - this is a deliberate act, which plays into the hands of our enemies.”
A number of foreign ministers from Germany, France, Russia and Ukraine agreed to push ahead with the withdrawal of heavy weapons from eastern Ukraine where violence has escalated after tough talks in Berlin.
"We agreed today not only to continue with the withdrawal of heavy weapons but also to include other categories of weapons in the withdrawal," German Foreign Minister Frank-Walter Steinmeier told reporters after the talks had finished, adding weapons to be withdrawn would now include tanks.
"Nothing is easy in the Ukraine crisis, this is not new. During these talks today the differences of opinion between Kiev and Moscow also became clear once again," he said, detailing an agreement between ministers at the talks.
The Ukrainian energy ministry has said in a statement that Ukraine has signed a new agreement to buy Russian gas over the next three months at $248 per thousand cubic metres.
The agreement extended all the other terms of the 'winter package' which has just lapsed between Ukraine's state gas concern Naftogaz and Russia's gas giant Gazprom, the statement said.
The agreement represented a "victory" for an economic approach to relations between Naftogaz and Gazprom over a political one, Energy Minister Volodymyr Demchyshyn was quoted as saying on the energy ministry's website.
US Vice President Joe Biden and Ukrainian President Petro Poroshenko have agreed that sanctions against Russia must be tied to the full implementation of the Minsk peace plan, the White House said.
"As long as Russia continues to fuel violence and instability in Ukraine, the international community must be prepared to increase the costs to Russia for pursuing such actions," a statement reads.
Biden also welcomed the decision by the Ukrainian parliament to allow special status for rebel-controlled eastern regions and grant them limited self-rule.
Biden and Poroshenko made the agreement in a telephone call.
The European Union has voiced deep concern at continuous military build-up and deterioration of human rights situation in the Crimea region of Ukraine.
"The European Union does not recognise and continues to condemn this act of violation of international law," EU foreign policy chief Federica Mogherini said in a statement marking the anniversary of Russia's annexation off the Ukrainian region. She said the EU would remain committed to its policy of not recognising the annexation, including through sanctions.
"The EU reaffirms its deep concern at the continuous military build-up and deterioration of the human rights situation in the Crimean peninsula, including the denial of free speech and the persecution of persons belonging to minorities," she said.
The relationship between Russia and the UK could be "prickly" for many years to come as the crisis in Ukraine continues, the Foreign Secretary has warned.
Speaking on the BBC's Andrew Marr show, Philip Hammond said Britain was prepared to escalate sanctions against Moscow if the Russia-backed separatists in Ukraine did not abide by the terms of the latest ceasefire.
He said under the rule of President Vladimir Putin, Russia had moved from being a partner of the West to viewing Europe as its "adversary" - and said he did not believe there was a "military solution" to the situation in Ukraine.
We have all made clear that if there is a big assault, for example on Mariupol, that will be responded to with a significant increase in the economic pressure on Russia from the EU.
Russia has decided that it wants to be in a strategic competition with the West, with Europe. It doesn't any longer see us as partners, it sees us as competitors or even adversaries and that means that we are going to have a difficult, prickly relationship with Russia probably for some time to come.
We don't think there can be a military resolution to this crisis. The disparity between the size of the Ukrainian armed forces and the Russian armed forces doesn't make that a sensible way to go.
We have to insist that the rules-based system which says very clearly that you can't change international boundaries by force, is protected.
Foreign Secretary Philip Hammond has said sanctions on Russia must remain in place and warned further sanction were possible if Russia does not comply with the Minsk agreement.
"The European Union will remain united on the question of sanctions, sanctions must remain in place until there is full compliance," Hammond said at a joint conference with his Polish counterpart in Warsaw.
"We will prepare possible new sanctions, which could be imposed quickly if there is further Russian aggression of if the Minsk agreement is not complied with," Hammond said.
More than 30 people have been killed in an explosion at a coal mine in the separatist stronghold of Donetsk in eastern Ukraine, Reuters reported, citing a local official.
"Rescue workers have not yet come to the place of the explosion, they are removing the poisonous gas and then will go down," Vladimir Tsymbalenko, head of the local mining safety service, said.
The Russian foreign minister has called on Ukraine to distance itself from 'extremists' and pursue a course towards peace.
Sergey Lavrov says 'tangible progress' has been achieved in implementing the package of measures agreed in Minks and the ceasefire is being consolidated.
A Ukrainian military spokesman said Ukrainian photographer Serhiy Nikolayev has been killed by shelling in east Ukraine despite a ceasefire deal.
"We don't know all the details, but there was shelling in Pesky today," spokesman Andriy Lysenko told Reuters news agency, saying the unnamed journalist had been taken to a military hospital where he died from his wounds.
Pesky is a government-held town on the front line, north-west of rebel-controlled Donetsk.