Ukrainian President Petro Poroshenko has warned that there are 9,000 Russian troops in the rebel-controlled area of eastern Ukraine and warned the country must be on alert for a large-scale attack.
Mr. Poroshenko made the comment to parliament Thursday, saying there exists a "colossal" threat of major new attacks.
He spoke a day after a major battle flared outside a main separatist stronghold in eastern Ukraine.
Firefighters scrambled to put out a fire at an open air market near Donetsk following a suspected rocket attack.
The Kremlin insists it has no direct role in the crisis, and has repeatedly denied supporting the rebellion with arms and fighters.
The truce signed by Russia, Ukraine, France and Germany in February required both sides to withdraw heavy weapons from the line of contact.
But international observers say those provisions have been routinely violated.