There has been a surge in violence between government troops and pro-Russian rebels in east Ukraine, despite diplomatic efforts to enforce a truce.
Ukraine said six government soldiers were killed in a 24-hour period and rebels said one of their fighters died in an army attack.
A BBC team witnessed exchanges of fire during a ceasefire monitoring mission.
On Monday, Ukraine, Russia, Germany and France called for the withdrawal of more weapons from the frontline.
The four nations also expressed "grave concern" over the surge in fighting.
A Russian military journalist was seriously wounded in the village of Shyrokyne, near the strategic port of Mariupol.
At the scene: BBC's Tom Burridge, Shyrokyne, eastern Ukraine
This was supposed to be a mission to monitor the ceasefire by a team from the Organisation for Security and Co-operation in Europe (OSCE).
We were told by the pro-Russian rebels, who guided us, and other journalists, that things were quiet in the village of Shyrokyne, near the strategic port city of Mariupol.
But within minutes of arriving, there are loud explosions. A man lies seriously wounded on the ground. He's bleeding badly from the head. We learn he's called Andrei and is a journalist working for Russia's military TV channel.
'Differences of opinion'
In Berlin, Ukrainian, Russia, German and French foreign ministers called for the withdrawal of mortars and heavy weapons with a calibre of less than 100mm, as well as all types of tanks.
German Foreign Minister Frank-Walter Steinmeier said all parties had reaffirmed the commitment to a ceasefire agreed in February in Minsk, Belarus, but that differences between Moscow and Kiev remained.
Both sides were largely thought to have adhered to the ceasefire deal - until a recent escalation of fighting near Donetsk and Shyrokyne.
Ukraine and the rebels both claim to have withdrawn heavy weapons from the line of contact but both sides have accused each other of planning fresh offensives and strengthening military hardware.
The Ukrainian government, Western leaders and Nato say there is clear evidence Russia is helping the rebels with heavy weapons and soldiers - an accusation echoed by independent experts. Moscow denies it, insisting that any Russians serving with the rebels are "volunteers".
More than 6,000 people have been killed in clashes since the rebels seized parts of eastern Ukraine last April - a month after Russia annexed Ukraine's southern Crimea peninsula.