
EU leaders meeting in Brussels also unanimously opposed "unilateral actions" by member states after Austria said it would cap the daily number of asylum claims.
The European migration commissioner has described the measure as "plainly incompatible" with European Union law.
Europe has "completely failed" in its response to the migrant crisis, UN High Commissioner for Refugees Filippo Grandi said in a German newspaper interview.
"We agreed that our joint action plan with Turkey remains a priority and we must do all we can to succeed," Tusk told a press conference after the first day of a two-day European Union summit in Brussels.
Merkel said the EU "must see quickly if measures work" under
the plan agreed at another EU-Turkey summit in November, in
which Turkey agreed to cut migrant flows in exchange for three billion euros in aid. ?AFP, BBC