The Iranian government is facing a new security challenge from a small, armed Iranian Kurdish group emboldened by the political gains of Kurds in neighbouring Iraq.

Pejak, the Party for a Free Life in Iranian Kurdistan, has emerged as behind recent unrest in the predominantly Kurdish north-west of the country, renewing a separatist armed struggle that halted a decade ago.

Of Iran's 70m population, about 10 per cent is estimated to be Kurdish.

Iranian Kurds were suppressed during Iran's 1979 revolution. But the main Kurdish opposition groups in the Islamic republic, including the Kurdistan Democratic Party of Iran (KDPI) and Komaleh, abandoned violence in the early 1990s and now advocate federalism.

However, unrest broke out last month after a Kurd named Shiwane Seyyed-Qaderi, who was not thought to be a political activist, was killed by the police in the north-western town of Mahabad, formerly a hotbed for Kurdish nationalism. Opposition groups published pictures of Shiwane's body on websites and claimed he was tortured to death. Four satellite Kurdish TV channels, based in Iraq and Belgium, broadcast the claims and fuelled anger in Iran.

Human Rights Watch claimed 17 died in the clashes, but local Kurdish groups say no more than eight were killed. Nevertheless, hundreds of Kurds were arrested and two Kurdish newspapers shut down.

According to Kurdish sources in Tehran, Pejak guerrillas joined the spontaneous protests. The media reported that the group killed four policemen and kidnapped another four. The captives were later released.

Tensions in Kurdish areas began to grow after the US-led invasion of Iraq two years ago gave Kurds a powerful voice in Iraq's postwar political process, including the installation of Jalal Talabani, the Kurdish leader, as president.

Iranian Kurds have also been watching Recep Tayyip Erdogan, the Turkish prime minister, who recently visited his country's predominantly Kurdish south-east and for the first time admitted wrongdoings by Ankara towards its restive minority.

Pejak is believed to be a sub-division of Turkey's outlawed Kurdistan Workers' party (PKK), which has been branded a terrorist organisation by the US and European Union. Its membership mainly comprises Iranian Kurds, but also includes some Turks and Iraqis.

"Pejak is a new phenomenon, and their identity and intentions still need to be investigated," Mohammad Karimian, the head of a 10-member Kurdish faction in Iran's 280-seat parliament, told the Financial Times.

Bahram Walad-Beigi, editor of Ashti, the Kurdish language daily closed during the recent unrest, estimates the number of Pejak guerrillas at about 500. These are believed to be based in a mountainous area close to the borders of Iran, Turkey and Iraq.

Iranian Kurdish activists fear that if the armed struggle gains momentum, it would give the regime an excuse to clamp down on Kurdish activists and deepen what ethnic Kurds see as discrimination.