TEHRAN (AFP) - Iranian police on Sunday shut down the office of a human rights centre headed by Nobel peace laureate and lawyer Shirin Ebadi on Sunday, in a sign of a toughening crackdown against rights campaigners. "They have sealed off the office and are telling us to leave the premises without resistance," the deputy head of Ebadi's Human Rights Defenders Centre, Narges Mohammadi, told AFP. "We have no choice but to leave." She said dozens of policemen had gathered in front of the group's office in northwest Tehran and that the officials had not "shown a judicial warrant but only provided the number of a warrant." She said policemen in uniform and plain clothes had raided the office and made an inventory of its contents. The group had been scheduled to hold a belated celebration marking the 60th anniversary of Human Rights Day on Dec 10. The closure marks a toughened crackdown on rights campaigners by the Islamic republic, which Ebadi's group accuses of "systematically violating" human rights. Ebadi condemned Sunday's crackdown but vowed that human rights advocates in Iran would be unfazed. "Shutting down the office without a warrant is illegal and we will protest," she told AFP by telephone. "Obviously such a move does not have a positive message for other rights activists in Iran, but my colleagues and I will fulfil our duties under any circumstances," she said. Founded by five prominent lawyers and headed by 2003 Nobel winner Ebadi, the group is a vocal critic of the human rights situation in Iran and has defended scores of prisoners of conscience, including high-profile dissidents and student activists. In an annual report in May Ebadi's group complained that "freedom of expression and freedom of circulating information have further declined" since President Mahmoud Ahmadinejad came to office in August 2005. "The lack of a real and effective observance of human rights deepens the gap between the people and the government and breaks the pillars of peace, stability and development in the country," it warned at the time. On Human Rights Day, Ebadi delivered a speech in Geneva calling for non-governmental organisations to be given a greater role in the UN's Human Rights Council and other bodies. The group holds frequent meetings on what it deems to be human rights violations. At one recent gathering, it renewed calls on Iran to stop executing people convicted of offences committed when they were minors.