Members of the ruling coalition have criticised Italy for sending weapons to Kyiv.
Italian Prime Minister Mario Draghi has won Senate support for his government's support for Ukraine.
Members of the coalition Five Star Movement (M5S) had called on Draghi to stop sending weapons to Kyiv and focus on diplomacy.
Their threat to split from Draghi's government could have destabilised Italian politics, but Draghi secured backing on Tuesday and thanked senators for their “united” support for the government line.
M5S leader -- and former Italian PM -- Giuseppe Conte has openly called for the country to stop sending weapons to Ukraine.
But the criticism has only created further divisions within the party, involving Italian Foreign Minister Luigi Di Maio.
Italy’s political landscape shifted on Wednesday after Di Maio formally announced his departure from the M5S, following disappointing results in recent local and administrative elections.
The party was founded in 2009 as an alternative to Italy's "establishment" political groups but has become fragmented since winning the most votes in the 2018 election.
Di Maio's new movement “Together for the Future” will be represented in the chamber with around 20 defecting MPs.
“We had to decide which side of history to be on,” the foreign minister told a late-night news conference
According to Italian media, several M5S senators will also join the party, meaning that the right-wing League holds a majority in parliament.
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