The following report is now a complimentary offering from MEMRI's Jihad and Terrorism Threat Monitor (JTTM). For JTTM subscription information, click here.
The multiple April 21, 2019 bombings in Sri Lanka, which targeted a number of churches and hotels, as well as other locations, and in which more than 200 people were killed and hundreds were wounded, appear to have been coordinated by a single organization. While no group has yet claimed responsibility for the bombings, many of which appear to be suicide attacks, supporters of the Islamic State (ISIS) have taken to Telegram to celebrate them. A Kashmiri pro-ISIS channel mentioned a poster that had been released on April 20, one day before the attacks, by the pro-ISIS Indonesian media outlet Ash-Shaff Foundation. The poster, showing a hooded man standing in front of the Notre Dame in Paris with a text threatening "lone wolf attacks" in "Crusader" churches,  seems to be a reaction to the April 15, 2019 Notre Dame fire. The Kashmiri channel, however, associated it with the Sri Lanka bombings, writing in English: "As-Shaff foundation (Pro Islamic State Media) had released a poster yesterday threatening of attacks and bloodshed in churches. And today three churches were attacked in Sri-Lanka, there is a possibility that Islamic State lonewolves executed this attack, but there is no claim from the official Islamic State sources." 
The pro-ISIS Muntasir Media Foundation released a poster celebrating the Sri Lanka attacks themselves. It shows a photo of one of the churches after the attack, with the caption: "Happy Easter to the Christians traitors of Jesus ('Alehi Asalam): Here is your Reward".
Another pro-ISIS media outlet, the Ash Shaff News Agency (which may or may not be linked to the Ash-the Shaff Foundation) celebrated the attack with several sarcastic posts. After providing information on the explosions in English and Indonesian, it commented: "What a great news and bad news for kuffar[unbelievers]. Ok Mr Kuffar, Welcome and enjoying in Jahannam [Hell]. HAHA..." In a later post, after quoting media sources that blamed the blasts on the Islamist group National Thowheed Jama’ath (NTJ), whose members include jihadis returned from Syria, Ash Shaff commented: "Ok Mr TerroriST what a great job, S A L U T E 4 You!" Following the seventh and eighth explosions, the media outlet posed: "Looks like the party is getting more exciting, nice weekend yaa Kuffar idiot! LOL".
ISIS supporter Al-Basha'ir wrote in Arabic on his own Telegram channel: "These burning churches, I think that terrorists are behind them, but Allah knows best. Notre Dame and now Sri Lanka."  Another pro-ISIS channel, Hamlat Fadh Al-Mukhabarat (The Campaign to Expose Intelligence Agents), published a gruesome photo of the carnage in one of the churches, with the Arabic text: "Preliminary photos of the celebration that was held today in the churches of Sri Lanka. We in turn congratulate them on this beautiful, festive day and ask Allah to repeat it on many days and for extended periods." 
The pro-ISIS Quraysh Media published a poster with the caption: "Sri Lanka pays the price. Islamic State."