LONDON (AP) — Britain's Secret Intelligence Service director used a rare public speech Monday to outline threats facing Britain and the need for more diversity in secret agent ranks.

MI6 chief Alex Younger, known by the code name "C'', told students at his alma mater, the University of St. Andrews in Scotland, that Britain will fortify its intelligence ties to European counterparts even though Britain is leaving the European Union next year.

"The implications of the Brexit debate have been set out by ministers," Younger said in his second speech since taking the top job at Britain's international intelligence service four years ago.

"For our part as SIS, we will always work with our sister agencies to strengthen our indispensable security ties in Europe."

He said adversaries like Russia view themselves as being in a state of "perpetual confrontation" with Britain and the West. He cited the "flagrant hostile act" of the use of the lethal nerve agent Novichok on ex-Russian spy Sergei Skripal and his daughter Yulia in the English city of Salisbury as a prime example.

The spymaster said MI6 helped expose the perpetrators and coordinate the expulsion of Russian diplomats from NATO nations and other allies that followed the British government's determination that the Russian state was likely behind the attack. The expulsions damaged Russia's intelligence gathering, he said.

"Our intention is for the Russian state to conclude that, whatever benefits it thinks it is accruing from this activity, they are not worth the risk," he said.

He encouraged students to seek employment at MI6 even if they don't fit the typical profile of an intelligence officer.

"I want to speak to young people who have never seen themselves in MI6. It doesn't matter where you are from," he said. "If you want to make a difference and you think you might have what it takes, then the chances are that you do have what it takes, and we hope you will step forward."

MI6 deals with international security challenges. The official threat level in Britain is set at "severe," indicating that intelligence analysts believe an attack is highly likely.