A fleet of Russian warships continued to steam south closer to the G20 host city of Brisbane on Thursday as experts stressed the show of force was aimed at the world as a whole, not just Australia.

Defence sources said the four ships, which include the Pacific flagship missile cruiser Varyag, were on a course that would put them in international waters off Brisbane by the time the international gathering gets under way on the weekend.

Prime Minister Tony Abbott played down the manoeuvre, saying it had nothing to with his recent vow to "shirt-front" Russian President Vladimir Putin over the downing of flight MH17.

But he pointedly noted the Kremlin had lately become more militarily assertive.

"We're seeing, regrettably, a great deal of Russian assertiveness right now in Ukraine," he said. "So it's not really surprising."

Australia has sent two Anzac Class frigates and a surveillance plane to monitor the Russians.

Opposition Leader Bill Shorten blasted the move as "a stunt".

"As far as I am concerned, this is a distraction from families getting closure by finding out why was that plane shot down, who knows what, who was involved in that terrible atrocity," he said.

A spokesman for the Russian embassy in Canberra insisted the move was a routine exercise to keep the navy fit and ready, and said Moscow had not needed to inform the Australian government because the ships were remaining in international waters – usually defined as at least 12 nautical miles (22 kilometres) from the coast.

Maxim Raku said Russia had interests in the southern hemisphere, even citing its global warming research facilities in Antarctica, as a reason why it needed to demonstrate its reach far from Russian territory.

"We are trying to widen our base because we have issues like global warming, scientific research in Antarctica, trade and international relations, so why not?"

Ross Babbage, a former government intelligence analyst and now defence scholar, said the display fit with the Kremlin's broader effort to show it was still a power to be reckoned with.

"What President Putin is trying to do is underline Russia's continuing status as a global superpower," he said.

Moscow has recently flown long-range bombers and surveillance planes in mock missions over Baltic countries and in the north Atlantic, in some cases triggering intercepts from Nato member states, he said.

Former Chief of Army Peter Leahy agreed Mr Putin's message was aimed at world powers who would be gathered in Brisbane for the G20.

"It's more about Russia saying to the global leaders, don't forget about us. We're not just known as a European power, we're also a Pacific power," said Professor Leahy, who is now head of the University of Canberra's National Security Institute.

 Lowy Institute military fellow James Brown said the move was a wake-up call for Australia because it was the "first tangible sign of this kind of strategic competition close to our own country".

The Russian arrival coincides with a visit to Stirling naval base in Perth by the United States nuclear submarine the USS Hawaii.

A defence source said it was possible that the fleet was being accompanied by a Russian submarine. This could draw attention to the lack of anti-submarine capabilities on the east coast as the government prepares to unveil its new Defence White Paper next year.

smh.com.au