Ukraine bloodshed
Ukraine marks 30 years since Chernobyl disaster
Ukrainian PM Volodymyr Groysman said lessons learned from Chernobyl should be heeded all over the world.
One serviceman from Ukraine's government forces had been killed and three others wounded.
Ukraine has repeatedly asked for international help to boost its defensive capabilities.
The threats came in statements issued after a video conference that brought together Obama and world leaders.
The exchange is one of the first moves to implement the peace deal reached on 2 February.
The Ukrainian Defence Ministry said 13 servicemen were killed and 157 wounded during the withdrawal.
Ukraine pulled thousands of troops out of the east Ukrainian town of Debaltseve on Wednesday.
Separatist forces fought their way into the key railway junction on Tuesday despite a ceasefire.
Kiev's position is worsening after the death of 10 civilians on the eve of peace talks.
Over 5,000 lives have so far been claimed in the conflict.
Fighting in eastern Ukraine is at its worst level since a ceasefire was agreed last September.
A 2-month-old ceasefire to end a war that’s killed 4,000 people appears shakier than ever.
Female fighters on both sides said the men in their units treat them as equals.
City authorities blamed the shelling on rebels and separatists blamed it on government forces.
A senior UN human rights official said on Monday that the actual figure may even be significantly higher.
Kiev's military said govt forces had clashed 26 times with separatists in the Russian-speaking east in 24hrs.
The expert group was the largest to access the wreckage since Flight MH17 crashed on 17 July.
The Dutch govt has urged Vladimir Putin to act quickly to allow access to the rebel-held crash site.
A summit of EU leaders is meeting in Brussels.