Ukraine army
Britain to step up training of Ukrainian armed forces
Some 200 Canadian troops will provide training in combat skills to Ukraine’s National Guard from August.
The threats came in statements issued after a video conference that brought together Obama and world leaders.
A military official said rebels had shelled Ukrainian positions 22 times over the past day.
The move was Kiev's most direct step to acknowledge that the ceasefire was finally holding
Fighting has eased in eastern Ukraine in recent days, raising hope that a ceasefire can finally take effect.
The Ukrainian Defence Ministry said 13 servicemen were killed and 157 wounded during the withdrawal.
Separatist forces fought their way into the key railway junction on Tuesday despite a ceasefire.
A Kiev military source said four Ukrainian soldiers had been killed and 21 wounded.
Over 5,000 lives have so far been claimed in the conflict.
Fighting raged in eastern Ukraine on Sunday between pro-Russian separatists and Ukranian forces.
Fighting in eastern Ukraine is at its worst level since a ceasefire was agreed last September.
Officials said rebels had carried out several small arms attacks on Ukrainian positions in the east.
Relations between the two have deteriorated since the overthrow of a Moscow-backed president.
Russia backs the separatists but denies it is directly involved in conflict in the Donbass region.
Loud explosions and artillery fire rocked Donetsk Airport in eastern Ukraine on Monday.
The flight went down in Ukraine on July 17, killing 298 people.
Dmitry Medvedev was quoted as saying sanctions must be abandoned to overcome problems with the West.
The past four days have seen the rebels stage elections for leadership which the government called illegal.
Separatist leaders accused Petro Poroshenko of suspending a law giving their regions “special status”.