Islamic State has claimed the deadly blast at a Shia mosque in Islamabad that killed 36 people, according to a PTI report. The blast happened during prayers at the Khadijatul Kubra mosque in the Tarlai area on Friday. IS called the attack a 'Fidayeen operation,' carried out by Saifullah Ansari, an IS soldier in Pakistan. The IS mouthpiece, Amaq, shared his photo and claimed over 200 casualties, much higher than Pakistan's official toll. IS also urged members of Lashkar-e-Taiba (LeT) to defect and join the Islamic State Khorasan Province (ISKP). This has caught the eye of Indian security agencies. Meanwhile, the Tehreek-e-Taliban Pakistan (TTP) denied any role in the attack. This blast is the deadliest in Islamabad since the 2008 Marriott hotel bombing. It coincided with Uzbek President Shavkat Mirziyoyev's visit to Pakistan and reflects rising sectarian tensions there. Earlier in January, ISKP claimed responsibility for a blast in Bajaur district that killed a senior LeT commander named Najibullah. The IS statement noted that hundreds of Pakistani Shias have joined the Iran-backed Zaynabiyoun brigade militia in Syria. The attack raises serious questions about Pakistan's ability to manage its security and growing sectarian violence.