BRUSSELS: German Chancellor Angela Merkel said on Friday the European Union must be ready to start returning migrants from Greece to Turkey rapidly to avoid a "pull factor" before the new system takes effect, although EU leaders had set no start date.

Speaking after an EU summit agreed on terms to offer Ankara later on Friday for a pact to fight irregular migration, she said negotiations with Turkish Prime Minister Ahmet Davutoglu would not be easy but that all EU countries wanted a deal.

"We did not set a date, but Turkey's clear understanding is that within a few days of returns starting, the one-for-one resettlement (of Syrian refugees from Turkey to Europe) should begin," Merkel told a news conference.