By Benedetto Cataldi BBC Monitoring

Castelli (left) is accused of helping Berlusconi

A fresh row over the business dealings of Prime Minister Silvio Berlusconi is shaking the Italian Government, with the centrist Union of Christian Democrats (UDC) threatening to quit.

Disagreements between the UDC and the Northern League - two of Italy's four ruling coalition parties - have undermined government unity several times since Italy took over the rotating presidency of the European Union (EU) in July.

The latest row erupted on Friday when the justice ministry blocked a request by Milan judges to carry out an investigation in the United States into alleged financial wrongdoing by Mediaset, Mr Berlusconi's media empire.

I have never seen a Christian Democrat resign and I do not believe he will resign Justice Minister Roberto Castelli

The quarrel has pitted Justice Undersecretary Michele Vietti, a UDC member, against his superior, Justice Minister Roberto Castelli, from the Northern League.

Mr Vietti said the block on trials of top state officials should be enforced "only after a request for a trial is lodged" and the measure "does not affect inquiries".

Minister's scorn

He threatened to resign if the justice ministry's intervention was not corrected, adding that the spat was affecting the entire ruling coalition.

The air is already too polluted for me to contribute to the pollution. Silvio Berlusconi

Mr Castelli reacted with scorn, saying: "I have never seen a Christian Democrat resign and I do not believe he will resign".

But the justice ministry's ruling has put him at the centre of a political storm.

The Left opposition has submitted a motion of no-confidence in Mr Castelli, which should be voted on next week, while the UDC has rallied to the defence of its junior minister.

Another UDC junior minister, Economy Undersecretary Gianluigi Magri, said that, should Mr Vietti resign, all the UDC ministers would follow him.

UDC leader Marco Follini issued an ultimatum for the justice minister, demanding that he lift the block on the inquiry into Mr Berlusconi's affairs by Monday.

Vietti is going against his boss, the justice minister

Lower House Speaker Pier Ferdinando Casini sided with the UDC and said that the government should honour its own pledges.

"The government in parliament... has declared certain things explicitly. The government must respect them, also because it has a duty of correctness," he said.

"The air is already too polluted for me to contribute to the pollution. I abstain from it."

What next?

If the deadlock is not broken, the government could find itself in deep trouble.

The UDC ministers could either resign or back the opposition's motion of no-confidence in Mr Castelli, thus forcing either themselves or the Northern League out of the coalition.

However, Italian President Carlo Azeglio Ciampi is unlikely to allow a full-blown government crisis during Italy's EU presidency.

Correspondents say the final reckoning for Italy's divided government could come in January 2004, when Ireland takes over the EU presidency from Italy.

BBC Monitoring, based in Caversham in southern England, selects and translates information from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages.