French President Francois Hollande and German Chancellor Angel Merkel have called on Ukrainian President Petro Poroshenko to ensure partial self-rule for the pro-Russian separatist east.
Poroshenko's office said the three had a telephone conversation on July 10.
It said Merkel and Hollande "recommended” that the Ukrainian president continue with constitutional reforms, adding that they "placed especial stress that the draft constitution of Ukraine reflects special self-rule for certain districts” of eastern Ukraine.
The peace deal signed in Minsk in February guarantees three years of self-rule to rebel-run parts of the Luhansk and Donetsk regions.
But Poroshenko's draft changes to the constitution only make reference to an existing piece of legislation that gives rebel leaders partial self-rule for an interim period of three years.
More than 6,500 people have been killed in fighting between Ukrainian government forces and the rebels in the country's east since April 2014.
Daily exchanges of fire have continued since the Minsk deal was signed.