German Chancellor Angel Merkel and French President Francois Hollande took the rare step Friday of pressing Ukraine's Western-backed leader to ensure partial self-rule for the pro-Russian separatist east.

The blunt message from two of Ukrainian President Petro Poroshenko's most important allies marked another sign of European impatience with fighting that still engulfs the ex-Soviet nation five months after the signing of a broad truce.

The 13-point agreement reached in the Belarussian capital Minsk controversially guarantees three years of autonomy to militia-run districts of Ukraine's industrial provinces of Lugansk and Donetsk.

The mostly Russian-speaking regions -- dotted with war-shattered steel mills and coal mines that once fuelled Ukraine's economy -- want their special status spelled out in constitutional amendments that would be enormously difficult to overturn.

But Poroshenko's draft changes so far only make passing reference to an existing piece of legislation that gives insurgency leaders temporary self-administration rights.

The rebels fear the law could be easily watered-down or even revoked -- a decision that would cheer Ukraine's nationalist forces and outrage Russian President Vladimir Putin.

The European Union's dire state of relations with Russia have been of particular concern to Merkel as she tries to return calm to the continent's jittery markets and bring more stability to the 28-nation bloc's eastern front.

Poroshenko said Merkel and Hollande -- both present at the Minsk agreement's signing in February -- had "recommended that the president of Ukraine continue with (his) constitutional reforms".

The two "especially stressed that the draft constitution of Ukraine reflects special self-rule for certain districts of the Donetsk and Lugansk regions".

Hollande's office confirmed that the French leader and Merkel placed "particular emphasis on the special status of certain areas in the regions of Donetsk and Lugansk in the draft constitution".