British intelligence agencies helped disrupt a plan to kill Western representatives in Libya and attack the country's interim leaders, Foreign Secretary William Hague said today.

In a rare speech on Britain's secret intelligence efforts, Hague also confirmed for the first time that agents from the MI6 foreign intelligence agency have died in recent years protecting the country.

Hague admitted that Britain's role in NATO-led intervention in Libya to protect civilians from late former strongman Muammar Gaddafi was "backed by effective intelligence" which "saved lives."

"For example the Gaddafi regime tried to attack the National Transitional Council in Benghazi, and to kill some of the Western representatives in Libya," Hague said in the speech.

"The agencies obtained firm intelligence, were able to warn the NTC of the threat and the attacks were prevented."

Britain had also disrupted a plot by extremists who travelled abroad for "terrorist training," Hague said, without specifying the country involved.

Speaking to an audience that included the heads of MI6 and the head of the domestic intelligence agency MI5, Hague paid tribute to those who served in Britain's secret services.

"Many agents and sources risk their lives -- some lose their lives -- to give us the vital information to keep us safe. We have a duty to protect them," he said.