TEHRAN, Nov 23 (AFP) - Iranian officials and newspapers on Monday condemned the murder of an ultra-nationalist opposition leader, saying it was a blow to the image of the Islamic regime.

Daryoush Foruhar, the head of the Iranian Nation's Party (INP) and a former labour minister, and his wife, Parvaneh, were stabbed to death by unknown assailants in their home here on Sunday evening.

Police have launched a manhunt for the killers.

The interior ministry issued a statement expressing regret over the killings and said it had launched an "extensive" investigation into the case.

Several newspapers also condemned the act.

"Foruhar is being murdered at a time when the country more than ever needs calm and to believe the humane face of Mr. Khatami's government," said the government daily Iran, referring to President Mohammad Khatami.

"The police and the judiciary must do their utmost to clarify the case," it said.

Even the hardline Jomhuri Islami, which was sharply critical of Foruhar's views, slammed the "ugly act."

"No matter what motivated it, this is an ugly act and must be condemned," it said. "This act is definitely taken by the enemies of the people with the aim of damaging the image of the Islamic regime."

"It is true that Foruhar was a dissident. But even dissidents have a right to voice their views within the law. And when they break the law, they should be dealt with within the framework of the law," the paper added.

Iran News called the murders an "abhorant crime," while another English-language daily, the Tehran Times, accused the Iraq-based armed opposition, People's Mujahedeen, of being responsible for the killings.

Foruhar, in his early 70s, had been an outspoken critic of the regime, accusing it of being undemocratic. He gave regular interviews to the Persian-language services of overseas radios.

A longtime prisoner of the Shah, he served as minister of labour in the interim government of Mehdi Bazargan who became prime minister after the 1979 Islamic revolution.

The transitional government was ousted after eight months and Foruhar has since been campaigning against the government.

Observers described Foruhar's murder as a severe blow to the secular opposition, which is already under mounting pressure from the regime.

Like other liberal and nationalist movements, the INP is banned but tolerated with activities limited to issuing statements, holding small private gatherings and having its leaders speak to foreign radios.

On Friday, two members of the liberal Islamic Iran's Freedom Movement were arrested in Esfahan, central Iran.

And a liberal personality, Ezatollah Sahabi,will stand trail on Monday, charged with printing lies and insults against the armed forces and provoking public disturbances.

Iranian leaders generally villify liberal movements, branding them as allies of Western powers bent on undermining the Islamic regime.

Foruhar was renowned for his strong nationalist sentiments and his abhorrence of the influence of Arab and Islamic culture in Iran.

Formerly the leader of the Pan-Iranist movement, he had forged close alliance with dissidents from non-Persian ethnic groups in Iran, notably the Kurds which have a history of struggle for autonomy.

His murder bears a shocking similarity to the assassination a decade ago in Paris of Shapur Bakhtiar, the last prime minister before the 1979 Islamic revolution.

Bakhtiar was stabbed to death along with his secretary by people who entered his suburban home in Paris as guests.

The two men were closely linked through years of shared opposition to the Shah's regime and both spent long stints in jail in the 1960s and 70s.

Almost all Iranian newspapers on Monday reported the couple's death.