By Paolo Biondi
ROME (Reuters) - The deputy head of Italy's fragile ruling coalition faced growing pressure on Wednesday to resign over the expulsion of a dissident Kazakh oligarch's wife and daughter, posing a threat to the stability of Prime Minister Enrico Letta's government.
Interior Minister Angelino Alfano, who also holds the title of deputy prime minister, told parliament on Tuesday that he had not been informed about the operation in which former Kazakh energy minister Mukhtar Ablyazov's wife and six-year-old child were detained in May.
The pair were bundled on to a private plane to Kazakhstan two days later - an unusually swift deportation that triggered speculation that Italy was trying to curry favor with energy-rich Kazakhstan.
Alfano faces a no-confidence motion on Friday called by opposition parties who have demanded his resignation, and for the first time on Wednesday they were joined by parliamentarians from partners in the ruling coalition.
"The position of Minister Alfano is objectively indefensible," a group of 12 senators from the center-left Democratic Party (PD) said in a statement.
The case has assumed ever more threatening dimensions for Letta's uneasy coalition, which was already struggling to contain tensions between the PD and Alfano's center-right People of Freedom (PDL), which has warned the government will fall if Alfano is forced out.
"If Alfano goes, the government will go 10 minutes later," senior PDL lawmaker Giancarlo Galan told RAI state television.
In the fevered climate of Rome politics, several PDL politicians say the case is being exploited as part of an internal power struggle within the PD by supporters of Florence mayor Matteo Renzi, who has openly declared his aim of becoming the next leader of the center-left.
They say Renzi's supporters, who include the 12 senators calling for Alfano to go, are stoking tensions with the aim of bringing down the government and causing new elections in the hope that Renzi would become prime minister.
Many details of the case remain unexplained. But Alfano's position received a further blow on Wednesday when a senior official, who resigned over the affair on Tuesday, said he had informed the minister of a meeting with the Kazakh ambassador to discuss the case.
The claim in the Corriere della Sera daily by Giuseppe Procaccini, former head of Alfano's office, cast doubt on the interior minister's account that he had not been informed by his staff even if it did not directly contradict the statement in parliament.
"What Procaccini has said makes the whole thing much more serious. I don't know what might happen between now and Friday," said one PD parliamentarian, who declined to be quoted by name.
Alfano told parliament on Tuesday that the operation was ordered after the Kazakh ambassador told Italian officials that Ablyazov, a former energy minister turned bitter critic of Kazakh President Nursultan Nazarbayev, was wanted in Kazakhstan on fraud and organized crime charges.
He said Italian police were told he was armed and dangerous however they did not know of his status as a dissident, and for that reason the case was not treated as a political issue.
Ablyazov himself was not present when the raid by around 50 police officers was carried out on the Rome villa on the night of May 28-29. He has since accused the Kazakh government of arranging to have his family "kidnapped".
Ablyazov fled Kazakhstan after his bank BTA was declared insolvent and nationalized in 2009 and was granted political asylum in Britain in 2011.
(Writing by James Mackenzie; Editing by Angus MacSwan)