Angela Merkel was under fire at home and abroad on Wednesday night as European Union leaders prepared to meet in Brussels on Thursday for a crunch summit to resolve their differences over the bloc’s three-year migrant crisis.

The German chancellor will arrive in Brussels with her Bavarian CSU coalition partners still threatening to pull down her government and Italy and other eastern EU states determined to defy her once unquestioned authority.

The EU summit comes after a turbulent week for Mrs Merkel that has exposed her growing weakness at home and apparently irreconcilable divisions in the EU over how to address the migrant crisis.

Donald Tusk, the European Council president, warned leaders that the debate was becoming “increasingly heated” and that the EU’s failure to defend its borders was handing winning arguments to populists with a “tendency towards overt authoritarianism”.

“The stakes are very high. And time is short,” he wrote in his invitation letter to leaders that also implicitly rebuked Mrs Merkel by warning Europe’s voters wanted to see leaders “restoring their sense of security” after the 2015 where EU borders were effectively thrown open by the German leader.

Europe’s internal divisions were highlighted again yesterday in horse-trading over how to deal with a rescue vessel in the Mediterranean carrying 230 migrants which had been refused permission to dock in Italy or Malta for the last six days.

Malta finally gave permission for the Dutch-registered Lifeline to dock, but only after eight EU states – France, Italy, Luxembourg, Portugal, Ireland, the Netherlands, Belgium and Malta –  agreed to take a share of the migrants.

Malta’s Prime Minister Joseph Muscat said the situation was “unique” and could not be considered a blueprint for handling future rescues, while Theo Francken, the Belgian minister for asylum and migration, said on Twitter it must be a “one-off operation”.

But Italy, which is demanding reforms to the EU’s Dublin rule that requires migrants to be registered in the first EU country they land in, hailed it as a political “victory” for its campaign to share out all new arrivals.

Matteo Salvini, Italy’s new hardline interior minister who has refused permission for NGO rescue ships to dock in Italy, heralded the deal as “another success of the Italian government”.

Germany was a notable absentee from the list of accepting states, however,reportedly at the insistance of Horst Seehofer, the hardline interior minister  from the Bavarian CSU who is demanding Italy and other EU states take back migrants who come north to Germany.

The scale of the task confronting Mrs Merkel was clear from remarks from the Italian prime minister Giuseppe Conte, who was cheered in parliament yesterday when he proclaimed: “Whoever lands in Italy, lands in Europe. Italy’s coasts are Europe’s coasts”.

The draft EU summit conclusions put heavy emphasis on bolstering the EU’s Frontex border force and creating ‘disembarkation platforms’ to off-load migrants back to non-EU states reflected the growing influence of hardline voices like Mr Seehofer, Mr Salvini and the leaders of Austria and Hungary who want the emphasis to be firmly on keeping migrants out.

Mrs Merkel is still calling for an “all European” solution to the migration crisis despite the vast differences between EU capitals making it virtually impossible for her to deliver on Mr Seehofer’s demand to get EU states to take migrants back or risk Germany unilaterally closing its border.

Such a move would risk a domino effect across Europe, threatening the EU Schengen free travel zone and forcing Mrs Merkel to sack Mr Seehofer, leading either new elections or creating an unstable minority government.

Talks between the coalition partners ended inconclusively in Berlin on Tuesday night, with Volker Kauder, a senior CDU member of parliament described the situation as “very serious”.