A month before the start of the Olympic Games, the chief of Britain’s domestic security service, MI5, offered a guarded reassurance on Monday about the risk of terrorist attacks during the 17-day spectacle in Britain, according to an article from The New York Times.

“No doubt some terrorists have thought about whether they could pull off an attack,” Jonathan Evans, MI5’s director general, told an audience in London. “But the Games are not an easy target, and the fact that we have disrupted multiple terrorist plots here and abroad in recent years demonstrates that the United Kingdom as a whole is not an easy target.”

British officials will deploy a security force of more than 25,000 for the Games, and Evans cited the “extremely generous” security assistance given by “friendly countries,” an allusion to an Olympic security unit run by FBI and CIA officials, the article says.

He said security officials had assessed the current threat of a terrorist strike in Britain as substantial, meaning that an attack is “a strong possibility.” But he noted that the threat assessment was “one notch lower” than it had been for most of the period since the 2001 attacks in the United States, according to the Times.

“There is no such thing as guaranteed security,” he said. “But I think we shall see a successful and memorable Games.”