Police detained three suspected Kurdish rebels allegedly planning an attack in Istanbul, an official said Saturday, while tens of thousands of Kurds across Turkey celebrated a spring festival traditionally used to assert separatist demands. Istanbul Gov. Muammer Guler said the three suspects had crossed into Turkey from northern Iraq over a month ago and were apprehended in the city before they could carry out an attack. Police seized explosives, a firearm, two hand grenades and three pistols, Guler said, but he did not give any information about the target of the alleged attack. Two of the suspects were detained Tuesday and the third was detained Saturday, he said. They are believed to be members of the Kurdistan Workers' Party rebel group, which has fought for autonomy in Turkey's southeast since 1984, leading to thousands of people being killed. The group carries out attacks from bases in northern Iraq, which borders Turkey. Police, who carried out the arrests this week on a tip-off, were also questioning three other people suspected of aiding the three alleged rebels.