Britain's MI6 chief to Russia: We will deter you

The chief of Britain's foreign intelligence service warned the Kremlin on Monday not to underestimate the West after a brazen nerve agent attack on a retired double agent in England stoked fears about Russian covert activity abroad.

In his second major speech since being named in 2014 to head the Secret Intelligence Service, MI6, Alex Younger said Russia has a stance of "perpetual confrontation" with the West.

"The Russian state used a military-grade chemical weapon on UK soil," Younger told students at the University of St Andrews in Scotland.

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

"I urge Russia or any other state intent on subverting our way of life not to underestimate our determination and our capabilities, or those of our allies," he said. "We do not seek to destabilise Russia." 

(With inputs from agencies.)