Italian Prime Minister Giuseppe Conte | Ben Stansall/AFP via Getty Images Italy stalls EU summit with block on joint conclusions ‘Nothing is agreed until everything is agreed,’ says Italian official.

Italy's new populist government sabotaged its first EU summit on Thursday, as Prime Minister Giuseppe Conte blocked all joint decisions ahead of a controversial dinner discussion on migration, several officials said.

Conte's refusal to accept the joint Council conclusions — written statements agreed by all leaders — even on noncontroversial topics prompted EU officials to scrap a planned evening news conference.

Italy had expressed its dismay over the trajectory of the migration discussion, but Conte's move to stall the entire summit caught other leaders off-guard.

According to one official observing the discussions, other leaders urged him not to block the other issues on which there appeared to be consensus — including strengthening defense cooperation, pursuing legislation that promotes digital innovation, and speeding work on the EU's next long-term budget — by linking them to the divisive migration debate.

The Italians are deeply angry that the discussion of migration policy has shifted in recent days away from its own concerns over the burden on frontline countries and focused instead on so-called "secondary movements," which had created a domestic political crisis for German Chancellor Angela Merkel.

The migration discussion was scheduled to be held over dinner — the time leaders traditionally reserve for their most difficult summit debates.

Council President Donald Tusk and Commission President Jean-Claude Juncker had scheduled a pre-dinner news conference where they planned to announce the agreement on other issues. But with Conte blocking everything, the news conference was cancelled.

"As one member reserved their position on the entire conclusions, no conclusions have been agreed at this stage," said a Council spokesperson, "For this reason, the press conference by the EU institutional representatives has been canceled and will instead take place tomorrow after the end of the Euro Summit."

The official observing the discussions said Tusk had conceded that according to Council procedures any one nation could block the conclusions, but that he also "encouraged everyone not to see this as the anticipation of a negative outcome, noting that there is a good possibility of a constructive outcome."

Conte's move appeared to confirm Brussels' worst fears that Italy's unusual coalition government — a partnership between the anti-establishment 5Stars and the Euroskeptic, hard-right League — could lead to paralysis.

An Italian official confirmed that the Conte was blocking agreement on the summit conclusions. "Nothing is agreed until everything is agreed," the official said.