The NIA has conducted searches at six locations in four districts of Tamil Nadu in a case related to Facebook posts by an extremist advocating the ideology of the Islamic State terror group and fundamentalist organisation Hizb-Ut-Tahrir, an official said on Sunday.

The searches were carried out in Thanjavur, Madurai, Theni and Tirunelveli districts at the residences of arrested accused Abdullah and his associates, the official of the NIA said.

In April, a complaint was received at Theppakulam police station that Abdullah had posted incendiary messages on Facebook, instigating people on religious grounds to wage war against India and establish Khilafat, thus threatening the unity, security and sovereignty of India, the official said.

The extremist advocated the ideology of the ISIS terror group and Hizb-Ut-Tahrir, the official of the premier investigation agency said.

An FIR was lodged by the Tamil Nadu Police in Madurai and the case was later taken over by the NIA.

During searches, 22 digital devices, including mobile phones, hard disks, memory cards, pen drives, laptops and many booklets containing incriminating materials have been recovered, the NIA official said, adding that further investigation in the case continues.