The UN Security Council scheduled an emergency session to discuss the fragile ceasefire in Ukraine on Friday, 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 triggered the worst standoff in East-West relations since the Cold War, came as the shaky ceasefire between Ukrainian forces and pro-Russian rebels appeared to be holding.
Ukraine's military said Thursday it had started withdrawing heavy weapons from the front line, bolstering a peace plan that was meant to come into force on February 15 but only took hold across the conflict zone in recent days.
The announced pull-back is a key part of a peace deal negotiated earlier this month in the Belarus capital Minsk.
"Ukraine is today (Thursday) beginning the withdrawal of 100mm cannons from the frontline," the army said in a statement.
"This is the first step in the pull-back of heavy weapons and will be carried out exclusively under the supervision and verification of the OSCE (the Organization for Security and Cooperation in Europe)."
US State Department spokeswoman Jen Psaki said that while there had been a reduction in fighting in recent days, the truce was still being broken.
"There are still violations... I wouldn't go so far as to call it a positive step," Psaki told reporters. "It's just a slight improvement."
An AFP photographer saw Ukrainian forces towing at least 15 cannon away from the frontline around the strategic town of Debaltseve.
The arms withdrawal, which is meant to create a buffer zone between the two warring sides, is due to be completed within two weeks.
Rebels insist they have already pulled back the majority of their artillery, rocket launchers and missile systems from some areas.
- Fighting dies down -
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.
While OSCE monitors have reported seeing some big guns heading away from the rebel lines, they say the warring sides have not provided information needed to determine what, if any, arms withdrawals have occurred.
Fighting has died down dramatically over the past few days. Ukraine's military said for the second day running that there were no fatalities among its soldiers but that four had been wounded.
NATO chief Jens Stoltenberg 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 in Rome.
"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.
Addressing US lawmakers on Wednesday, Secretary of State John Kerry said Russia and the pro-Moscow rebels had failed to meet the terms of the ceasefire and renewed warnings that Russia could face further sanctions.
But Moscow says threats of new punishment are evidence that the West is not interested in the success of the latest effort to stop fighting that has cost at least 5,800 lives since April.
- Threat to gas supplies -
"Behind these calls lies the unwillingness of... the United States, the European Union, to seek the implementation of what was agreed," Russian Foreign Minister Sergei Lavrov said.
Russia 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.
That threat prompted the EU to invite the Russian and Ukrainian energy ministers to Brussels on Monday for talks on resolving the dispute. Ukraine's gas company Naftogaz confirmed it would attend the talks as part of a Ukrainian delegation.
EU foreign policy chief Federica Mogherini "touched on" the gas issue in a call with Lavrov, her office said in a terse statement.
The West says the best hope for a negotiated solution to the 10-month conflict lies with the truce, which last week won unanimous backing from the UN Security Council.
But breaches by rebel forces -- especially their assault on Debaltseve, a strategic transport hub, and attacks on Ukrainian army positions near the port city of Mariupol -- have exasperated the EU and US.
The peace plan also entails a series of subsequent steps including the start of discussions on handing over greater autonomy to the rebel regions and the reinstatement of Kiev's control over swathes of its border with Russia.  
Source: AFP