The pope's representative in Britain has urged Roman Catholics to form a "united front" with Muslims and Jews to oppose gay marriage, a media report said on Saturday.
Archbishop Antonio Mennini has called for closer co-operation with other faiths to put pressure on the British government over its plans to allow same-sex couples to marry, the Telegraph reported.
In an address to Catholic bishops, he reiterated recent comments by Pope Benedict who said the church faced "powerful political and cultural currents" in favour of redefining marriage.
Muslim and Jewish leaders reportedly intervened after equalities minister Lynne Featherstone launched a national consultation on how same-sex marriage might be introduced.
The Muslim Council of Britain has voiced opposition to the plans. It described the plan as "unnecessary and unhelpful", the report said.
In Scotland, the Council of Glasgow Imams have reportedly agreed on a resolution describing same-sex marriage as an "attack" on their faith and fundamental beliefs.
In the Jewish community, the Liberal and Reform synagogues have given their support to same-sex marriage but rabbis within the main United Synagogues have expressed opposition, the daily said.
Rabbi Yitzchak Schochet of Mill Hill United Synagogue in London recently accused the government of launching an "assault" on religious values.
Lord Indarjit Singh, head of the Network of Sikh Organisations, has said the proposed reforms represented "a sideways assault on religion".