CNN  —  An international roaming outage is leaving customers of the three major US mobile carriers in the dark, making it difficult or impossible for American customers who are currently out of the country to make calls, send messages and use data. AT&T, T-Mobile and Verizon confirmed to CNN that their customers are experiencing intermittent issues while traveling overseas. “We’re one of several providers impacted by a third-party vendor’s issue that is intermittently affecting some international roaming service,” a T-Mobile spokesperson told CNN. “We’re working with them to resolve it.” Meanwhile, Verizon told CNN about 30% of its customers’ calls and data connections from overseas are not going through right now. The issue stems from an international third-party communications provider called Syniverse, which manages international roaming connections for various carriers. In a company statement, Syniverse said it started to experience connectivity issues affecting mobile users early Thursday morning. “Since the onset of these issues, Syniverse has been working closely with our network partners to restore full service,” the statement said. “We understand the inconvenience this has caused and appreciate your patience as we navigate this challenge.” The company did not elaborate on the cause of the issue.