ROME (Reuters) - Italian Prime Minister Matteo Renzi stepped up his attacks against other European Union leaders on Sunday after an EU summit in Bratislava which he said amounted to no more than "a nice cruise on the Danube."

Renzi said at the end of Friday's summit he was dissatisfied with its closing statement, after he was excluded from a joint news conference by German Chancellor Angela Merkel and French President Francois Hollande..

In particular, he criticized the lack of commitments on the economy and immigration in the summit's conclusions, which he himself signed.

In a fiery interview in daily Corriere della Sera on Sunday Renzi - who has staked his career on a referendum this year on his plan for constitutional reform - intensified his criticisms, though he remained vague on what commitments he would have liked the summit to have produced.

"If we want to pass the afternoon writing documents without any soul or any horizon they can do it on their own," Renzi said of his fellow leaders.

"I don't know what Merkel is referring to when she talks about the 'spirit of Bratislava'," he said. "If things go on like this, instead of the spirit of Bratislava we'll be talking about the ghost of Europe."

Renzi has promised to resign if he loses the autumn referendum and is preparing a 2017 budget which he says will cut taxes despite a slowing economy and record high public debt.

"At Bratislava we had a nice cruise on the Danube, but I hoped for answers to the crisis caused by Brexit (Britain's exit from the EU), not just to go on a boat trip," he said.

He was similarly belligerent about the budget to be presented next month, saying there would be "no negotiation" with Brussels, and money he planned to spend on tackling immigration and making Italy safer from earthquakes would be excluded from EU rules on deficit limits.

Other countries were more guilty than Italy of breaking budget rules and Italy had met its commitments on tackling the inflows of migrants crossing the Mediterranean, Renzi said.

"I'm not going to stay silent for the sake of a quiet life ... if someone wants to keep Italy quiet they have picked the wrong place, the wrong method and the wrong subject."

With polls showing the referendum too close to call, Renzi insisted he had "never been so optimistic" about its outcome. The ballot is expected to be held in late November or early December.

The other EU leader to most vocally criticize the results of the Bratislava summit was Hungarian leader Viktor Orban, who faces his own domestic referendum next month, on the EU's plan to relocate refugees throughout the continent.

(Reporting By Gavin Jones; Editing by Ros Russell)