Ukraine troops shelled by pro-Russian rebels near Mariupol
Pro-Russian rebels have shelled Ukrainian army positions east of the key city of Mariupol in breach of a ceasefire deal, the BBC has witnessed.
Our correspondent was with Ukrainian troops when they came under heavy fire moments after a team of international monitors left the area.
This comes a day after the US accused Russia of sending more troops to the region. Moscow denies any involvement.
A truce between the two sides in the conflict was brokered in February.
But two Ukrainian soldiers told the BBC's Tom Burridge that the fighting has continued despite the agreement signed by Ukrainian forces and pro-Russian rebels in Minsk.
Our correspondent says that after the most intense shelling had died down, they were shown a large unexploded shell that had apparently smashed through the upstairs wall of the building.
Its size suggests it was fired from a heavy weapon, the type that should have been withdrawn from the frontline under the Minsk agreement, our correspondent adds.
At the scene: Tom Burridge, Shyrokyne, near Mariupol
The dimly-lit, musty, concrete building we were cowering in with Ukrainian troops rattled as the shells rained down. First they felt close, shock-waves that penetrated the ground, and reverberated around us.
But then you started to feel the impact vibrate through your body. It was relentless, as every few moments another hit. The initial period of shelling went on for about an hour, before the Ukrainian forces started firing back.
However during that period the Ukrainian troops sat, slept and rolled their eyes. This, they said, was routine.
Viktor, 28, who not long ago worked for British American Tobacco in Dubai, said it was a "lie" that there was peace in this region.
Simon, another soldier, aged 22, said that the amount of fighting on this part of the frontline had actually increased since the Minsk peace deal was made in February.
As a journalist covering the conflict in Eastern Ukraine I'm used to being bombarded with information, unverified claims, and accusations from both sides.
However what we witnessed suggests the rebel forces east of Mariupol have little appetite for peace, and throws more doubt on the ability of Russia and European leaders to resolve this conflict.
The US state department on Wednesday accused "combined Russian-separatist forces" of violating the terms of Minsk by keep artillery and multiple rocket launchers in prohibited areas.
Spokeswoman Marie Harf also accused the Russian military of deploying "additional air defence systems into eastern Ukraine" and moving several of them "nearer the front lines".
The "increasingly complex nature" of the training of separatists "leaves no doubt that Russia is involved", she added.
"After maintaining a relatively steady presence along the border, Russia is sending additional units there. These forces will give Russia its largest presence on the border since October 2014."
The Kremlin has not yet responded to the US claims.
The Ukrainian government, Western leaders and Nato say there is clear evidence that Russia is helping the rebels with heavy weapons and soldiers. Independent experts echo that accusation. Moscow denies it, insisting that any Russians serving with the rebels are "volunteers".
Earlier this month, about 300 US paratroopers arrived in western Ukraine to train with Ukrainian national guard units.
At the time, Kremlin spokesman Dmitry Peskov warned the move "could seriously destabilise" the situation in Ukraine.
One of the key points of the Minsk deal stipulates that all foreign armed groups, weapons and mercenaries should withdraw from Ukrainian territory.
The UN says at least 6,116 people have been killed since the fighting began in the Donetsk and Luhansk regions last April - a month after Russia annexed the Crimean peninsula.