An ultranationalist party headed by the Israeli Foreign Minister said yesterday that it has prepared legislation linking citizenship to an oath of allegiance, in what amounted to a threat to the country's Arabs to swear loyalty to the Jewish state or risk severe punishment.

The bill follows a separate proposal on Sunday by the same party that would make it illegal for Arabs to mourn the "catastrophe" – the term Palestinians use to describe their defeat and exile in the war that surrounded Israel's founding.

Both proposals by the Foreign Minister Avigdor Lieberman's Yisrael Beitenu party focus on the perceived disloyalty of the country's Arab citizens, roughly a fifth of Israel's population of seven million.

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The loyalty oath was one of the central planks in Mr Lieberman's campaign for February's parliamentary elections. The legislation, which must pass several hurdles yet to win approval, drew harsh criticism from opposition legislators and civil rights groups.

Mohammed Darawshe of the Abraham Fund Initiatives, which works for peaceful co-existence between Jews and Arabs in Israel, said the bills reflect "an ideology imported from dark regimes that have collapsed".

Yisrael Beitenu won third place in the February elections with a message that suggested Israel's Arabs were an internal threat to the country. It is a senior partner in the coalition government and was largely supported by Israelis who, like Mr Lieberman, are immigrants from the former Soviet Union.

The party says it will present its proposed loyalty oath to a ministerial committee for preliminary approval on Sunday. The legislation would make citizenship contingent on an oath of loyalty to Israel as a "Jewish, Zionist and democratic state," said party spokesman Tal Nahum. The bill would make it possible for the government to revoke the citizenship of anyone who does not comply or perform some form of military or national service.