The UN Security Council on Friday was to hold an emergency session on the fragile truce in Ukraine, a year to the day since Russian troops and pro-Moscow forces began seizing ports and cities on the Black Sea peninsula of Crimea.
The anniversary of the seizure, which sparked the worst East-West standoff since the Cold War, came as a shaky ceasefire between Ukrainian forces and pro-Russian rebels appeared to gain traction.
Both sides said they were continuing to withdraw heavy weapons from along the frontline, a key part of a stuttering peace plan aimed at ending ten months of bloodshed in east Ukraine that has cost some 5,800 lives.
Kiev said Thursday that it had started withdrawing 100-mm cannons, while rebels claim they have nearly completed their pull-back.
Monitors from the Organization for Security and Co-operation in Europe (OSCE), however, told AFP that while they have seen weapon movements on both sides it was too early to confirm that a full withdrawal was taking place.
The situation on the ground remains intensely fragile and Ukrainian President Petro Poroshenko cautioned the withdrawal was "just a first, test step".
"At any moment our soldiers are ready to return our weapons to their previous positions and rebuff the enemy," Poroshenko told troops in a speech Friday.
The pull-back, which is meant to create a buffer zone between the two warring sides, is supposed to be completed within two weeks.
Diplomats at the United Nations said the Security Council would hold an emergency session on Friday on the ceasefire deal at the request of France and Germany.
Council members will hear a report from two OSCE representatives on the situation on the ground, before holding talks behind closed doors.
Fighting has died down dramatically under the ceasefire deal that was meant to start February 15 and for the third day running neither side reported any fatalities.
US State Department spokeswoman Jen Psaki warned however said that while there had been a reduction in fighting in recent days, the truce was still being broken.
NATO chief Jens Stoltenberg has hailed the downturn in violence but kept up the pressure by calling for Moscow to pull out of Ukraine the weapons it is accused of sending in to the rebels.
"Russia has transferred in recent months over 1,000 pieces of equipment -- tanks, artillery and advanced air defence systems," Stoltenberg said.
"They have to withdraw this equipment and they have to stop supporting separatists."
The words highlighted how tense relations between the West and Moscow have become since Russia's annexation of Crimea -- when the Kremlin at first denied sending in troops to seize territory before later admitting it had lied.
Both the United States and European Union have renewed warnings that Moscow -- which has already seen tough sanctions and falling oil prices batter its economy -- could face fresh economic punishment if the peace process unravels.
But Moscow says the threats are evidence that the West is not interested in peace and has itself ratcheted up the pressure by warning it could cut off gas supplies to Ukraine -- and, by extension, to parts of the European Union.
Ukraine and Russia confirmed that they would attend an urgent EU-brokered meeting in Brussels Monday to try to resolve a dispute related to Moscow's move to start direct supplies to rebel-held areas.
Moscow last year cut off gas deliveries to Ukraine before turning the taps back on in December after making cash-strapped Kiev pay in advance for its supplies.
Now Russia's state-owned gas giant has warned that Ukraine has only coughed up enough money to cover gas supplies to the end of the week.
"If the money does not arrive in time, gas will not be delivered," Gazprom spokesman Sergei Kupriyanov said in a statement.
Ukraine says that Russia has masterminded the rebellion in the east to punish Kiev for a historic shift towards the West that started with the ouster of Kremlin-backed leader Viktor Yanukovych last February, only to be followed up by the annexation of Crimea.
The Kremlin claims it acted to protect Russian-speakers in Crimea after what it paints as an illegal right-wing coup in Kiev.
The West is hoping the UN-backed truce deal can prevent the crisis between the once-close ex-Soviet nations escalating further.
The peace plan entails a series of tricky steps including discussions on handing over greater autonomy to the rebel regions and the reinstatement of Kiev's control over swathes of its border with Russia.
Short link: