German Chancellor Angela Merkel and French President Francois Hollande will meet in Berlin to give a new push to European efforts to tackle the biggest migrant crisis in 50 years.
The pair will also hold talks on the resurgence of violence in Ukraine, and will be joined by that country's president Petro Poroshenko later in the day.
Merkel and Hollande have put enormous political onus on resolving Ukraine's 16-month pro-Russian uprising and returning peace to the European Union's turbulent eastern front.
Monday's talks will be notable for their exclusion of Russian leader Vladimir Putin.
The French and German leaders negotiated a peace deal with Putin and Poroshenko in February, which promised to end the fighting quickly and resolve all political disputes by the end of the year.
Yet the so-called Minsk II accord has repeatedly been broken by the warring sides.
The death toll in the war is meanwhile steadily approaching 6900.
A Ukrainian source said Putin's exclusion pointed to the fact that "France and Germany are in the same boat as us", but a French source quickly quashed any interpretation of a "diplomatic war against Russia".
The diplomatic push on migrants meanwhile comes as the EU is grappling with an unprecedented influx of people fleeing war, repression and poverty in what the bloc has described as its worst refugee crisis since World War II.
Official figures show a record 107,500 migrants crossed into the EU last month, and there are mounting calls for Europe to adopt a more unified approach in dealing with the influx.
"There has to be a new impetus so that what has been decided is implemented," a source in the French presidency said, referring to EU decisions taken in June to tackle the crisis.
"The situation is not resolving itself," the source said, adding that the decisions made by the EU "are not sufficient, not quick enough and not up to the task".
Their priorities include compiling a list of countries whose nationals would not be considered asylum seekers except in exceptional personal circumstances.
The French and German leaders will also move to help speed up the setting up of reception centres in overwhelmed Greece and Italy - two countries that have borne the brunt of the crisis - to help identify asylum seekers and illegal migrants.