[UPDATE] Business Insider reports that Pokemon Go’s international rollout to countries like the United Kingdom and the Netherlands has been paused. Niantic CEO John Hanke told them that it’s “hard at work on a fix” and the rollout will be “paused until [it’s] comfortable.” While the United States has been able to download Pokemon Go, it’s still unavailable in Canada.

Original story: Perhaps as a result of its tremendous popularity, Pokemon Go players have been encountering serious server issues. After staying mostly silent since its launch in the United States this week, its developer has now spoken out about the problems.

“Thank you for your patience,” a tweet from the official Pokemon Go account states. “We have been working to fix the server issues.”

These issues have manifested themselves in a number of ways. Many are unable to log into the game, while others can do so but run into trouble when actually trying to catch Pokemon.

The tweet goes on to promise the game’s rollout will continue in “new countries soon.” It’s possible the game’s release in countries like Canada has been held up while developer Niantic attempts to address the server issues.

The problems come as something of a surprise considering the game has been in testing in various markets around the world for months. But Go has proven to be extremely popular, rising to the top of the iOS charts. Nintendo’s stock price has risen in the wake of the game’s release, although it’s actually The Pokemon Company (of which Nintendo is a co-owner) and Niantic that are responsible for its development.

Police and state officials have warned players about paying attention to their surroundings while playing, and in a bizarre story, a young woman may have discovered a dead body as a result of the game.

For more on Pokemon Go, check out our roundup of everything you need to know.