Italy's new government won a confidence vote in the upper house Senate on Tuesday allowing it to take office following a stormy debate, with Prime Minister Giuseppe Conte and his former deputy Matteo Salvini accusing each other of betrayal.

Conte, backed by the anti-establishment 5-Star Movement and center-left Democratic Party (PD), won an initial confidence motion in the lower house on Monday, meaning his coalition can now forge ahead with its pro-European agenda.

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It clinched the Senate vote by 169 to 133. The result effectively gives Conte an eight seat majority in the 321-seat chamber, meaning it might struggle to push forward legislation on particularly divisive issues like immigration.

Once bitter enemies, the 5-Star and PD unexpectedly agreed to join forces last month after the far-right League walked out of the previous coalition with 5-Star in a failed attempt to trigger snap elections.

League leader Salvini, who served as deputy prime minister and interior minister in the last administration, had hoped to cash in on his surging popularity in the opinion polls, but now faces the prospect of 3-1/2 years in opposition.

Relations between Salvini and Conte, a law professor with no party affiliation, have grown fraught and the two men exchanged insults in a rowdy session of the usually sedate Senate.

"Prime Minister Conte, I do not envy you," Salvini said. "You got your position through betrayal. I couldn't sit there even for 15 minutes. I don't have power, but I have my dignity and the affection of the Italian people."

Conte said that by attempting to "unilaterally and arbitrarily" bring about early elections Salvini had acted with "arrogance and little knowledge of constitutional law."