Britain is prepared to strike first to defend itself against a cyber attack from an enemy state, Foreign Secretary William Hague said Tuesday.

His warning was the first clear signal that the UK has developed new weapons for the online battlefield.

Hague told The Sun that the globe was in the grip of a new and financially-crippling "arms race in cyberspace."

He said he could not guarantee that Britain would be able to repel a major cyber assault on the nation's essential infrastructure -- including water works, power plants and the air traffic control system.

But he said, "We will defend ourselves in every way we can, not only to deflect but to prevent attacks that we know are taking place."

Hague gave no clues on the makeup of Britain's new electronic arsenal, saying, "The rest of the world will have to guess."

The British government is pouring an extra £650 million ($1 billion) into developing deterrents to hostile viruses, which are being produced almost constantly.

"We are trying to prevent an arms race in cyber space," Hague said. "Given that the Internet changes every day, and billions more people will have access to it over the coming years, the potential for that arms race to grow and go out of control is enormous."

He added, "There is no 100 percent defense against this, just as there isn't against any other form of attack. We have to defend critical national infrastructure. We have to defend national security. We have to defend our entire commercial and economic system."

Hague spoke ahead of a cyberspace conference. Senior officials from more than 60 nations and bosses of online giants will meet in London next month to discuss the cyber menace and draw up an "international rule book" on how best to fight it.