A top European Union official has pressed leaders of the 28 member states to live up to pledges to tackle the refugee emergency and said their credibility is at stake if they fail to act during today's summit meeting.

European Commission president Jean-Claude Juncker said "the member states have got to do what they promised to do".

Mr Juncker said that "it's a question of credibility, of ... whether they can live up to their promises".

Mr Juncker's statement came as EU leaders converged on Brussels for a summit focused on the refugee crisis.

The leaders promised last month to massively step up spending and provide more experts to help fingerprint and screen the thousands of people arriving in Europe daily seeking refuge or jobs.

But few countries have come forward with money or personnel.

Earlier, German chancellor Angela Merkel said Europe must co-operate with Turkey in order to tackle the migrant crisis.

She said that by improving conditions in those regions where migrants come from they may be dissuaded from travelling to Europe.

She told German politicians that "without doubt Turkey plays a key role in this matter" because it hosts almost two million Syrians and is a key transit point for migrants coming to Europe.

Ms Merkel, who travels to Istanbul on Sunday, said talks with Turkish leaders will not tie co-operation on the refugee issue to the country's future membership of the European Union.

The European Commission complained that only three of 28 nations have pledged a total of just 12 million euro to a fund to help African nations better manage their borders. The pot is meant to total 1.8 billion euro over two years.

The EU's border agency and asylum office have appealed for a total of around 1,000 officers to help fingerprint people and decide whether they are eligible for asylum.

So far, about a dozen of the 28 EU nations have offered around 130 personnel.

"We can, and must, do much better," said EU president Donald Tusk.