Prime Minister Mario Draghi insisted yesterday that Italy's parliament was sovereign after the Vatican made an unprecedented complaint about a draft law against homophobia.

"What I want to say, especially concerning the latest developments, is that ours is a secular state, not a confessional state," said the premier, a practising Catholic.

"So parliament is free to debate - obviously, these are obvious considerations - and to legislate," he added, addressing the Senate.

Mr Draghi was reacting to news that the Vatican had lodged a diplomatic protest in the form of a "note verbale" against the so-called Zan law.

The proposed law seeks to punish acts of discrimination and incitement to violence against gay, lesbian, transgender and disabled people.

But the Vatican argued that it violates the Concordat, the bilateral treaty between Rome and the Holy See, by curtailing Catholic freedom of belief and expression, according to the Corriere della Sera newspaper.

It expressed concern that because of the Zan law, Catholics could in the future face legal action for expressing their opinions on LGBTI (Lesbian, Gay, Bisexual, Transgender and Intersex) issues, the newspaper said.

"Our legal system contains all the guarantees to make sure that laws always respect constitutional principles and international commitments, including the Concordat with the Church," Mr Draghi said.

The centre-left lawmaker who is sponsoring the bill, Alessandro Zan of the Democratic Party, rebuffed the Vatican's arguments on Tuesday.

"The text [of the law] does not restrict in any way freedom of expression or religious freedom," he tweeted, adding that there should be "no foreign interference" in the activities of a sovereign parliament.

The Zan law was passed by the lower house of parliament in November, but it faces stiff opposition from Matteo Salvini's League party and other right-wingers in the upper Senate.

Mr Draghi's government - an awkward national unity coalition including critics and supporters of the Zan law - has no official position on the bill.