Rory McIlroy and Justin Thomas have supported the PGA Tour's decision to suspend all players competing in the LIV Golf Invitational Series.

PGA Tour commissioner Jay Monahan sent a memo to all members on Thursday confirming the news, shortly after LIV Golf's first event had launched at Centurion Club near London.

All 17 Tour members competing in the first Saudi-backed tournament of the breakaway series, including six-time major winner Phil Mickelson, were informed they are no longer eligible to play in events on the circuit.

The memo warned that any player featuring in future LIV events will face a similar punishment.

McIlroy said on Wednesday he understands why some have made the switch due to the huge sums of money on offer, but the Northern Irishman is pleased with the decision to block players from competing on both circuits.

"I think at this point, Jay [Monahan] has been pretty transparent in terms of he's just going to act within the tournament regulations and the rules that are set for a PGA Tour member," McIlroy said.

"All he's doing is basically going by the book. I think that the majority of the membership that are here this week and that haven't gone and played elsewhere really appreciate that.

"So, I think he's done the right thing because these guys have broken rules and done things outside of the tournament regulations, and because of that, there are going to be consequences, I guess."

McIlroy was speaking after carding an opening-round 66 at the RBC Canadian Open on Thursday, with Thomas three shots further back.

While the four-time major winner is against the idea of the breakaway series, he will be tuning in out of curiosity.

"I think like everyone else, I'm intrigued and I'm a fan of golf," McIlroy said. "I've got quite a few guys over there that I call friends that are playing. 

"Yeah, of course I'll see it and watch it and see what all the fuss is about."

Mickelson is the highest-profile casualty of Thursday's announcement, with Dustin Johnson and Sergio Garcia having already notified the Tour that they have resigned their membership.

Louis Oosthuizen, Lee Westwood and Ian Poulter are among the other notable names featuring at the three-day LIV Golf Invitational London event that will have 12 teams and 48 players.

Echoing the comments made by McIlroy, Thomas said: "I'm pleased. I think anybody that's shocked clearly hasn't been listening to the message that Jay and everybody's been putting out. They took that risk going into it, whether they thought it was a risk or not.

"Like I've said the whole time, I have great belief and great confidence in the PGA Tour and where we're going and continuing to grow to, and those guys just aren't going to be a part of it.

"[LIV Golf] are obviously throwing so much money at people that it's very hard to turn down. I don't care what you say in terms of that people play for different reasons. It doesn't matter who you are or what it is, everything has a number.

"They're reaching that number for some people, and I hope that they don't get others. But I think a very strong core group of us is very stable and firm in our position, and I hope that it stays that way."