Justin Bieber announced on Monday that he has decided to cancel the remainder of his Purpose World Tour dates due to “unforeseen circumstances.” So what exactly could have led him to do so?

Insiders close to the Bieber camp tell PEOPLE the 23-year-old singer is “okay for now,” but is “super exhausted” from his previous tour dates and the extensive travel that comes along with his scheduling.

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“He’s been going to church and has been hanging out with his church crew. He’s super exhausted though,” a source tells PEOPLE of Bieber’s current state. “He actually does like being on tour, but he’s been touring for 18 months straight and it takes a toll.”

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In a statement on Monday, the star’s rep shared: “Due to unforeseen circumstances, Justin Bieber will cancel the remainder of the Purpose World Tour concerts. Justin loves his fans and hates to disappoint them. He thanks his fans for the incredible experience of the Purpose World Tour over last 18 months. He is grateful and honored to have shared that experience with his cast and crew for over 150 successful shows across six continents during this run. However, after careful consideration, he has decided he will not be performing any further dates. Tickets will be refunded at point of purchase.”

A specific reason for Bieber’s decision was not provided, and a rep for Bieber did not immediately reply to PEOPLE and Entertainment Weekly’s request for comment.

The cancellation will impact ticket holders of over a dozen upcoming concerts, including a Dallas show scheduled for Saturday. Bieber was also slated to play the Rose Bowl in Los Angeles and shows in New York, Minneapolis, Boston, and Toronto before heading to Asia for a handful of concerts in Japan, the Philippines, and Singapore.

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The Purpose tour marked the Canadian pop star’s third world tour; the extended jaunt kicked off on March 9, 2016 in Seattle and took Bieber all over North America, Asia, Europe, Africa, and Latin America.

“This is a guy who has had 150 shows on this tour, on six continents, over the last year and half, and he’s tired,” a source told Entertainment Tonight. “He needed a break and as much as he didn’t want to disappoint his fans, the best decision for him was to cancel the remaining tour dates … The tour was just really long and he was exhausted.”

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Bieber was spotted in Santa Monica, California, on Monday afternoon shortly after the announcement.