UK military commanders said Britain's newest aircraft carrier, HMS Queen Elizabeth, has taken on the "lion's share" of operations against ISIS in Iraq.
In the first posting of the 65,000-tonne carrier, commanders said the ship attracted the interest of Russian warplanes.
“At the moment, we’re taking on the lion’s share of that operation over Iraq, which is a fantastic feather in our cap," said Commodore Steve Moorhouse, aboard carrier in the Eastern Mediterranean Sea.
Cdre Moorhouse said the Eastern Mediterranean had become more “congested and contested” because of Russia’s military presence in Syria.
“We’re rubbing up against Russian activity, not in a dangerous or aggressive manner, but you’ve just got other people out here playing in what is a fixed piece of water and airspace,” he said.
Cdre Moorhouse said a Russian warship came within 10 kilometres of the carrier.
He said Russian, British and US pilots had a “healthy respect for one another” and their conduct had been “absolutely professional” since the aircraft carrier started anti-ISIS operations on June 18.
"But there is a reality when you buy yourself a fifth-generation aircraft carrier and you take it around the world," Cdre Moorhouse said. "People are interested in it."
Capt James Blackmore, who commands the eight F-35 jets and 10 helicopters on the vessel, said British and Russian pilots had come within visual distance of each other.
“It’s that cat-and-mouse posturing. It’s what we expect in this region of world,” Capt Blackmore said.
He said it was the first time F-35s were used in the Eastern Mediterranean.
“So, of course Russia wants to look at what they’re like," Capt Blackmore said. "They want to look at what our carriers are like."
Meanwhile, UK Foreign Secretary Dominic Raab arrived in South-East Asia for a three-day visit to Vietnam, Cambodia and Singapore for talks on trade, defence and security.
The Foreign Office said Mr Raab's visit came "at a time of growing defence and security co-operation with the region".
"The UK is committed to strengthening our friendship across the Indo-Pacific," Mr Raab said.