Italy's civil aviation regulator said today it might sue Irish low-cost carrier Ryanair Holdings Plc for libel in a row over security check-in documents.

The Irish airline said last week it would stop domestic flights at 10 Italian airports from January 23 because of reduced security in check-in measures. Ryanair objects to a decision by ENAC, the civil aviation body, to lower requirements on documents presented by passengers. ENAC Chairman Vito Riggio told Reuters he was studying possible cases of libel against Ryanair. He said security standards at Italian airports were certified by international bodies.

"Their statement is defamatory and damages the image of our country and affects the government as a whole," Riggio said in a telephone interview.

He added that if Ryanair cut its domestic flights in Italy, other operators would replace it.

Ryanair said today it has been forced to cancel its domestic routes in Italy because the new rules do not provide adequate security compared with international standards.

The airline will resume domestic flights as soon as the new identification requirements are removed by ENAC, it said in a statement.

Ryanair, which only accepts passports and ID cards on its flights, has said the documents which ENAC had approved included fishing permits and company IDs.

ENAC has invited Ryanair's representatives to a meeting in Rome on January 7 to discuss the issue.