U.K.’s exit from the European Union would significantly weaken the bloc’s security, David Petraeus, a former U.S. military commander and CIA director, wrote in the Sunday Telegraph newspaper. A Brexit would do nothing to reduce the risk from terrorism and other global threats in Britain, Patraeus wrote.

“I encourage my British friends to think twice before withdrawing from one of the most important institutions that undergirds Western strength: the European Union,” Patraeus wrote. “A Brexit would also reduce considerably Great Britain's ability to influence and guide the future of Europe, still the world's largest economic bloc; it would undoubtedly reduce British influence on the world stage, as well.”

Britain will vote in a referendum on whether to stay in or out of the EU on June 23. According to polls, cited by Reuters, support for an exit was rising though many voters remain undecided.

Patraeus also echoed the British government's key arguments in its campaign to convince voters to stay in the EU, and said that though a retreat into the "perceived safety of isolation" was tempting, history had shown such decisions were a strategic dead end.

The U.S. general’s Sunday comments disputed earlier comments by Michael Hayden, ex-director of the CIA and the National Security Agency, who said Friday that leaving the EU would have a limited impact on British security. Former U.K. foreign intelligence chief Richard Dearlove has also reportedly said that there could be security gains from an exit, according to Reuters.