Rome, Jul 16 (IANS/AKI): A senior conservative senator in Italy has sparked calls for his resignation after he likened integration minister, Congo-born Cecile Kyenge, to an orangutan.

"When I see images of Kyenge, I cannot help but think, even if I don't say that she is one, of a resemblance to an orangutan," Roberto Calderoli, leader of Italy's anti-immigrants Northern League party and vice president of Italy's upper house, said at a party rally.

Prime Minister Enrico Letta immediately termed Calderoli's comments as "unacceptable" and "beyond all limits", in a message on his official Twitter account.

He urged Northern League party secretary Roberto Maroni "to resolve this shameful matter immediately".

The country's head of state, President Giorgio Napolitano, said he was "indignant" at "the very serious episode... which shows the growing barbarity of public life".

Members of the Democratic Party demanded Calderoli's resignation while politicians from former premier Silvio Berlusconi's conservative People of Freedom Party voiced "solidarity" with the 48-year-old Kyenge.

Trade unions, consumer groups and the Jewish community in Italy also condemned Calderoli while consumer group Codacons announced it would take legal action against his racist remarks.

Kyenge, who has been campaigning to make it easier for migrants to gain citizenship, told AKI she felt "bitter regret" at Calderoli's words.

"Constructive criticism of politicies is welcome, while insults are not," she said.

Meanwhile, in an interview with Corriere della Sera daily, Kyenge said she received threats over the phone and the internet "daily".

Prosecutors are investigating a series of threats made against the minister by far-right groups.

Calderoli initially tried to shrug off the senator's comments, telling Italy's Radio Capital they had been "a joke".

But she later said he had phoned Kyenge to apologise.

Calderoli, a former minister, has caused offence several times in the past.

In 2007, he threatened to walk his pet pig over land earmarked for a mosque in the northern city of Bologna. In 2006, he was forced to resign as reform minister after he displayed a T-shirt allegedly mocking Islam.