Lionel Cironneau, Associated Press
Migrants sit at the Franco-Italian border near Menton, southeastern France, Sunday, June 14, 2015. Some 150 migrants, principally from Eritrea and Sudan, attempted to cross the border from Italy and have been blocked by French and Italian gendarmes.

VENTIMIGLIA, Italy — Italy warned retaliation Sunday against the European Union if governments don't make good on proposals to take in more asylum seekers as migrants desperate to reach northern Europe camped out for a third day along borders tightened by Italy's northern neighbors.

Premier Matteo Renzi threatened an unspecified "Plan B" if the EU doesn't show more solidarity with Italy, which has borne the brunt of rescuing migrants at sea and providing initial assistance to them at overflowing reception centers across the country.

Renzi's interior minister, Angelino Alfano, said Sunday that the EU would find "a different Italy" if it doesn't endorse a refugee redistribution plan at an EU interior ministers' meeting this week in Luxembourg. He said he would also press for European help repatriating migrants who don't qualify for asylum, saying Italy had borne the cost last year of sending back nearly 16,000 migrants who were passed over for refugee status.

"I will say with great clarity: Kids, either we do equal distribution of migrants in Europe, or we organize refugee camps in Libya, or we organize a serious policy of repatriation," Alfano told Sky TG24. "If Europe doesn't follow through on its responsibility and solidarity, it will find a different Italy."

The diplomatic wrangling came as migrants continued to languish at key points along Italy's border with its northern neighbors after French police blocked border crossings last week, including at Ventimiglia, near the swank resorts of Nice and Saint-Jean-Cap-Ferrat on the French Riviera.

"Where are human rights? Where is humanity? It is a big problem for us," said Naser Alden Abdulaziz, a migrant from Darfur, Sudan who was among about 200 people, most from Sudan, Libya and Eritrea, who protested for a third day at the Ventimiglia border.

Denied crossing to France, they have been camped out for days on the rocky seafront or in the shade of trees outside the train station, where local residents have been helping Red Cross workers distribute food.

The French Interior Ministry said it had reinforced border controls over the last few weeks due to an influx of migrants. Elsewhere along Italy's northern frontier, Austria increased its border surveillance after neighboring Germany initiated border stops for the recent G-7 summit of industrialized nations and the international Bilderberg conference this weekend in Bavaria.

Under EU rules, would-be refugees are supposed to be fingerprinted and apply for asylum in Italy since it's the first EU country where they land. Many new migrants, however, prefer to slip through Italy without being officially registered so they can head to destinations further north where there might be better job opportunities while their asylum claims are processed.

As a result, the tightened border closures have created a backlog at Italian frontier crossings and train stations, with migrants still hoping to continue their journeys north rather than settle in Italy. On Saturday, officials in Rome and Milan took emergency measures to accommodate the swelling crowds, setting up tents outside a Rome train station and fixing up a former canteen near Milan's station.

The European Commission had proposed that EU governments endorse its scheme to share responsibility for taking in 40,000 recently-arrived Syrian and Eritrean would-be refugees. But diplomats say nearly half of the EU nations are insisting that the scheme be voluntary, not mandatory, and that the proposal could be watered down at Tuesday's interior minister meeting in Luxembourg.

Renzi balked at even the original Commission proposal, saying it was "almost a provocation" to take in so few migrants given that so far this year some 57,167 people had arrived in Italy as of June 13. The figure was slightly up from the 53,827 who arrived in the same period in 2014.

"In the coming days, Europe's identity will be in play, and our voice will be heard since we're a founding member," Renzi warned in Corriere della Sera. "If the European Council chooses solidarity, good. If not, we have our 'Plan B,'" he said, without elaborating.

Winfield reported from Rome.