The European Union's eastern members agreed that should a deal with Turkey to stem the flow of refugees into Europe fail, the bloc should have a "plan B" that would seal Greece's northern borders.

Leaders of the Czech Republic, Slovakia, Poland and Hungary, meeting in Prague three days before an E.U. summit, offered troops, police and other aid to Macedonia and Bulgaria, which border Greece, to keep refugees from continuing their journey to the heart of the continent. While leaders stopped short of suggesting an immediate cutoff of Greece from the visa-free Schengen area, they said a plan B should be ready by April.

"We are waiting for the results of the E.U.-Turkey pact," Slovak Prime Minister Robert Fico said Monday. "There are attempts to make it work. But if this attempt fails, we won't have an alternative other than drawing a new Schengen border. Our stance in Brussels will be that we want a plan B."

Europe's refugee crisis has divided the E.U. and is threatening borderless travel within the Schengen area, a principle that underpins the 28-nation trading bloc. While German Chancellor Angela Merkel has been trying to form a "coalition of the willing" that would accept refugees, the bloc's eastern members steadfastly refuse to do so, and want migrant flows into the trading bloc via the Balkans halted.

The leaders in Prague affirmed their support for an initiative that's angered Germany, the desired destination for most of the refugees, which has been trying to persuade other E.U. members to accept bloc-wide quotas for settling migrants. The Slovak government received a complaint from the German ambassador over the weekend, Fico said.

More than 76,000 migrants and refugees have crossed from the shores of Turkey to Greek islands this year, up from less than 5,000 in the same period in 2015, according to the United Nations' refugee agency. A record 856,000 people arrived in Greece by sea last year, U.N. data show, most of them making their way toward central Europe via Macedonia, the former Yugoslav republic to the north.

The E.U. has tried to seal a deal with Turkey, which initially promised to crack down on human traffickers and keep the refugees — primarily from Syria, Afghanistan and Iraq — on its territory in exchange for 3 billion euros ($3.35 billion) in aid. The agreement has so far failed to deliver results, with tens of thousands of people still braving the sea to the Greek islands. Syrian government forces, with Russian air support, have encircled Aleppo, threatening to ignite the exodus of thousands from the rebel-held city.

Merkel last week met with Turkish Prime Minister Ahmet Davutoglu and said the only way to end the flood of illegal immigrants was to allow the E.U. to screen refugees on Turkish soil and bring in legally those who qualify for asylum.

Greece's government has dismissed criticism of its handling of the crisis, saying that the sheer size of the problem overwhelms the country's resources. The government in Athens said its navy vessels can't use force against plastic boats carrying unarmed refugees, including women and children. It also accused European governments of having failed to fulfill their commitments to accept thousands of refugees.

"This is the largest population movement since World War II," Greek Deputy Prime Minister Yannis Dragasakis said in an interview with the Athens-based To Vima newspaper published Sunday. "Europe hasn't presented a unified, comprehensive policy on the basis of its humane ideals."