JERUSALEM – Islamic State sympathizers and militants celebrated last night’s deadly terrorist massacre at a crowded concert in Manchester, England, with the jihadists vowing to continue the onslaught against the West.

The Islamic State claimed that a “soldier of the caliphate planted bombs in the middle of Crusaders gatherings,” apparently taking credit for the carnage.

Breitbart Jerusalem obtained access to correspondence posted in a closed chat group that utilizes the encrypted Telegram messaging service. The chat group serves as an internal Twitter of sorts for IS jihadists and sympathizers, and it has been used in the past to issue IS communications.

A militant named Abu Ayman Alalmani (the German) wrote, “Thanks to Allah who allowed this achievement of the Mujahedeen. We are all believers in Allah that our brothers, the supporters and the Mujahedeen, are those who committed the attack among the infidels. We swear to Allah that the infidel countries in the West won’t have the luxury of security. This is a Godly promise and this is the promise of the Mujahedeen, the future will prove to you that you are the countries of heresy. You will see this and not only hear it.”

An account titled “Muslim Justice” wrote, “Allah is great, Allah is great, we will shake the infidel and criminal regimes. We will destroy the rule of those who abandon Islam [a reference to Arab leaders]. Allah is great, this is a call that will rise high on the horizon and we will yet defeat the cross and the countries of infidels.”

ISIS member Abu Abdullah Alsury (the Syrian) wrote, “Thanks to Allah who caused the faithful to rejoice, we ask and request of Allah that this blessed act will be part of the battle of our brothers, the lone wolves roaming across all parts of the infidel nations, as they seek this type of blessed attack. This is part of the work and this is part of the revenge. Those infidel states will pay a heavy price.”

Prior to the Islamic State claiming credit for the attack, another militant, Alqaqaa Alidlebi from Idlib, wrote, “We’re waiting for our brothers in the official media department to publish what should warm our hearts with an official declaration of responsibility, even if this isn’t an organized act.”

“We pray to Allah that the attacker is a faithful Muslim. You aren’t aware of the huge happiness here in the ranks of the Mujahedeen and their families in the district of Elkheir (the area of Dir Azzur on the border between Syria and Iraq). How happy we are that Allah guided the hand of the attacker to send the heads of the corrupt infidels who murder the Muslims in our countries flying.”

Aaron Klein is Breitbart’s Jerusalem bureau chief and senior investigative reporter. He is a New York Times bestselling author and hosts the popular weekend talk radio program, “Aaron Klein Investigative Radio.” Follow him on Twitter @AaronKleinShow. Follow him on Facebook.

Ali Waked is the Arab affairs correspondent for Breitbart Jerusalem.