VIENNA (REUTERS) - An Austrian minister has received death threats for allowing refugees into the country, government sources said on Tuesday, amid a raging debate over the rights and duties of Muslims and immigrants in the predominantly Roman Catholic country.

The Interior Ministry sources said two letters sent to the ministry and broadcaster ORF said Interior Minister Johanna Mikl-Leitner and 50 other politicians from the ruling coalition and opposition Greens would be killed if Mikl-Leitner let in more refugees.

Austria, with 8.5 million residents, received around 17,500 asylum requests in 2013, mostly from Russia, Afghanistan and Syria, according to official statistics. The federal government and local politicians have been squabbling over the refusal of some provinces to fulfil quotas for accommodating refugees.

A spokeswoman for Vienna prosecutors said they had opened an investigation but declined to describe the nature of the threats against Mikl-Leitner, a member of the conservative People's Party (OVP) that rules in a coalition with the centre-left Social Democrats (SPO).

The threat against the politicians comes as opinion polls show Austria's far-right Freedom Party is neck and neck with traditional centrist parties, attracting about a quarter of votes on its anti-immigration platform.

Three weeks ago Austria proposed legislation to prohibit foreign funding of Muslim organisations and to push for standardised German-language translations of the Koran, in a move aimed in part at tackling Islamic extremism.

Officials suspect around 150 people from Austria have joined up with jihadist militants fighting in the Middle East.