Italy's Five Star Movement, the biggest party in Prime Minister Mario Draghi's government, on Tuesday looked on course to split over long-running tensions exacerbated by attitudes to the Ukraine war.
Dozens of lawmakers have signed up to form a new group led by Foreign Minister Luigi Di Maio due to launch in 2023, media reports said.
Di Maio has backed Draghi's policy of supporting Kyiv and sending weapons to Ukraine.
The former Five Star leader and deputy prime minister has clashed for months with the head of the party, former premier Giuseppe Conte.
Conte argues that Italy's efforts should instead focus on a diplomatic solution.
Tensions peaked at the weekend after Di Maio called for an end to party criticism over Draghi's approach to the Ukraine crisis - notably the sending of weapons to Kyiv.
"I am accused by the leaders of my political force of being Atlanticist and pro-European," Di Maio wrote in a statement.
"Let me say that, as foreign minister, in the face of this terrible war I proudly claim to be strongly Atlanticist and pro-European."
A diplomatic solution
Conte has warned against Italy getting involved in an arms race.
"We have contributed by sending three lots of weapons, now it seems to us our contribution would be more precious on the diplomatic front," he said earlier this month.
Draghi's government has sent weapons and cash to help Ukraine, while strongly supporting EU sanctions against Russia.
Despite the friction, lawmakers in the Senate agreed by 219 votes to 20 a majority resolution Tuesday in support of Draghi's policy.
The compromise resolution grants more involvement by parliament in decisions, including over weapons shipments - something sought by Conte.
Ahead of the vote - which came ahead of a June 23-24 EU Summit - Draghi made clear his course was set.
The former European Central Bank chief, who visited Kyiv last week with the leaders of France and Germany, recalled lawmakers' majority vote in March to send weapons.
"Italy will continue to work with the European Union and with our G7 partners to support Ukraine, to seek peace, to overcome this crisis," said Draghi, with Di Maio at his side.
"This is the mandate the government has received from parliament, from you. This is the guide for our action."
Five Star (M5S) once threatened to upend the political order in Italy, taking office after winning a third of the vote on an anti-establishment ticket in the 2018 election.
But recent dismal showings in opinion polls suggest it will sustain heavy losses in national elections next year.
Despite being riven with splits and defections, Five Star is still part of a national unity government led by Draghi.