Geelani, Ayaz Akbar and Altaf Ahmad Shah were detained as they were leaving for Eidgah martyrs' graveyard to pay tribute to the youths killed during the 2010 summer agitation, a spokesman of the Hurriyat said.
Police said that the trio was taken to Humhama police station and lodged there.
They said Geelani and his aides were taken into preventive detention as their presence in the old city could have lead to disturbance of peace in the area.
