Ruptures are starting to show in Italy’s populist coalition as anti-immigration moves by Matteo Salvini, interior minister and leader of the far-right League, unsettle senior politicians from his ally, the Five Star Movement (M5S), and the party’s core voters.

Voters from across the political spectrum flocked to the anti-establishment movement founded by TV comedian Beppe Grillo in 2010. They were attracted by its stance on corruption, but also by the party’s pledge to help small businesses, slash red tape and lift people out of poverty, and by its emphasis on the environment.

But two months into the M5S-League coalition government some have major doubts. Last week Roberto Fico, M5S MP and president of the chamber of deputies, spoke out against a controversial pact with Libya that sees migrants forcibly returned to war-riven north Africa.

On the night of 30 July, according to the International Organization for Migration, almost 350 people were taken back to Libya. Fico commented: “Libya is not a safe landing point. Human rights are not guaranteed, so migrants cannot be left there.”

He has also clashed with Salvini over his xenophobic rhetoric and blocking of Italian ports to rescue ships. “I don’t want to close the ports,” he said. “We need to talk about immigration with intelligence and heart.”

Other M5S politicians have come forward as attacks on immigrants have risen. There have been 12 shootings, two murders and 33 physical assaults in the two months since Salvini became interior minister. “All of us, starting from those in the political world, have the responsibility to create a barrier to these unacceptable, cowardly episodes,” M5S MP Vincenzo Spadafora said last Monday.

Discontent is also simmering among M5S voters, particularly in the party’s southern stronghold of Campania, where Fico and party leader Luigi Di Maio are from.

“I was against M5S collaborating with the League,” said Paolo Silletti of Caserta, near Naples, “mainly because I hate Salvini. For years he insulted people from the south. Many others I know who voted for M5S also do not like the coalition; the two parties don’t have many points in common.”

M5S supporters were also unhappy about a proposal last week by Lorenzo Fontana, the families minister from the League, to scrap the anti-fascist Mancino law, passed in 1993 to outlaw racist violence and hate speech. Di Maio was quick to point out, via Facebook, that this was not part of the coalition’s plan. Many responded with online comments lambasting the government. “Be quiet before many of us repent for having given you our vote, only to find homophobes and xenophobes in government,” said one.

Di Maio has been silent on immigration, referring to Fico’s stance as his “personal opinion”. Giuseppe Conte, the unknown professor M5S and the League agreed on as prime minister, has so far had little sway over the two party leaders.

Other M5S MPs are taking a neutral approach, arguing that the party must honour the immigration policy agreed in the coalition deal. This included plans to clamp down on migration across the Mediterranean, and to accelerate deportation of an estimated 500,000 illegal immigrants.

“We need to implement what we wrote in the joint programme,” Laura Castelli, undersecretary for the economy ministry, told the Observer.

Piera Aiello, MP for the Sicilian city of Marsala, said that going back on the agreement could jeopardise other joint policies. “Rightly, we’re not for absolutism or just abandoning people,” she said. “But at the same time we can’t say ‘everyone’s welcome’, only to cast people aside like urchins. Yes, we need to act with humanity, but the responsibility needs to be shared across Europe.” Rino Marinello, an M5S senator also from Sicily, said Salvini’s initiatives were a result of mistakes by the previous leftwing government. “Immigration here has not been well managed – people come, but they have no opportunities to work or build a life,” he said. “Opening our ports while the rest of Europe shut theirs was a problem. Our priority should be developing a policy that improves lives for people in Africa.”

Immigration is a thorny topic, but unlikely to break the coalition in the short term. “There may be people who don’t agree with Salvini, but this is part of the game,” said Mauro Calise, a politics professor from Naples. “Both sides need each other and nobody is going to make a single issue enough of a reason to break anything. Moreover, Salvini’s policy [to reduce immigration] has been successful – he’s basically continuing what [predecessor] Marco Minniti did, the difference being that Salvini has been very good at communicating it.”