David Leavitt, a Boston-based freelance journalist, was slammed on Twitter for joking about Ariana Grande’s music after Tuesday night’s blast at the singer’s concert at Manchester Arena, northern England. The explosion killed 19 people and around 50 others were injured, according to Greater Manchester Police.

The blast happened at about 10:33 p.m. local time (5:33 p.m. EDT). Local police said they are treating the incident as a terrorist attack until they find otherwise. Following the blast, Leavitt took to Twitter to comment on Grande’s music.

A screenshot of freelance journalist David Leavitt's tweet on blast at Ariana Grande's concert at Manchester Arena, England, May 23, 2017.

However, his tweet didn't go down well with fellow Twitter users and received a backlash from them.

Leavitt issued an apology for his comment and deleted the tweet after several social media users forced him to do so.

“Sorry 4 offending. Didn’t realize the magnitude of the tragedy. I always make stupid jokes about whatever's trending. Condolences 2 families,” he said in a tweet.

Leavitt’s bio on his Facebook account stated he has a Bachelor of Arts in Humanities and Social Sciences from the University of Massachusetts Dartmouth. His bio said he wrote over 3,000 articles in his career so far. Leavitt’s Twitter bio said he works at CBS, AXS, Yahoo and the Examiner as a freelance writer and reviews games, technology, fashion, and travel. After his tweet, CBS’ Boston affiliate WBZ said Leavitt was not employed by the station.

“David Leavitt is not a WBZ employee. His abhorrent comments in no way represent the views of our station,” WBZ wrote on Twitter.

AXS also distanced themselves from Leavitt.

“This person is not employed by AXS. We don't endorse this despicable comment,” AXS wrote on their Twitter account.

Meanwhile, Greater Manchester Police is investigating the blast. Two U.S. law enforcement sources told CBS New York the explosion was carried out by a suicide bomber who traveled to Victoria Station near Manchester Arena by tube, or subway. The bomber then went to the ticket area and detonated the explosive when people began to leave the concert, the report said, citing sources. Officials in Manchester are tracking movements of the alleged suicide bomber through surveillance footage. Another source told the news outlet that parts of the bomber have been recovered.

In recent years, terrorist threat level in Britain has been set at “severe” indicating that an attack is most likely possible. If the latest blast is confirmed as a terrorist attack, it would be the most fatal in Britain since the London subway bombings in 2005 in which over 50 civilians were killed.

In the latest blast, witnesses reportedly heard two loud bangs near the arena’s bars. Grande reacted on Twitter following the incident. A representative for Grande said she was fine after the explosion.

The 23-year-old’s tour began February 3 in Arizona. She was scheduled to perform at Belgium, Poland, Germany, Switzerland and France after the Manchester concert. She also had concerts scheduled in Latin America and Asia. The singer has indefinitely suspended her world tour following the blast, TMZ reported late Tuesday.

"We mourn the lives of children and loved ones taken by this cowardly act. We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers," Grande’s manager, Scooter Braun, said.