By Paul Sandle

GLASTONBURY, England, June 23 (Reuters) - Johnny Depp courted controversy at Britain's Glastonbury music festival with a joke about assassinating Donald Trump, pondering how long it had been since an actor had killed a U.S. president.

Depp, 54, was speaking to a crowd on Thursday evening as he introduced a screening of his 2004 film "The Libertine" at the music and performing arts festival. Discussion turned to the topic of U.S. President Trump.

"It is just a question, I'm not insinuating anything... When was the last time an actor assassinated a president" Depp asked the audience, in a possible reference to actor John Wilkes Booth, who assassinated President Abraham Lincoln in 1865.

"Now I want to clarify, I'm not an actor. I lie for a living. However, it's been a while, and maybe it's time."

Depp's comments come less than a month after comedian Kathy Griffin drew strong criticism for posing in photographs holding up the likeness of a bloody, severed head resembling Trump. CNN ultimately fired Griffin from its annual New Year's Eve broadcast over the controversy.

Last week, a gunman shot at Republican lawmakers who were practising for a charity baseball game.

The Secret Service said in a statement to ABC that it actively monitored open source reporting, including social media networks and evaluates potential threats.

"For security reasons, we cannot discuss specifically nor in general terms the means and methods of how we perform our protective responsibilities," the Secret Service said.

Depp, the face of the Pirates of the Caribbean movie franchise, seemed aware his comments might spur controversy.

"This is going to be in the press," he said before making the comments. "It will be horrible."

(Reporting by Paul Sandle and Brendan O'Brien; Writing by Alistair Smout; editing by Guy Faulconbridge and Ralph Boulton) ((alistair.smout@thomsonreuters.com; +44 207 542 7064; Reuters Messaging: alistair.smout.thomsonreuters.com@reuters.net))