The Prime Minister also says the onus should now be put squarely on Russia to play the key role in forging a political solution and bringing the Syrian war to an end after President Trump's response to the use of chemical weapons.

While he conceded that the fate of Assad would be decided by the global and regional parties to any settlement, Mr Turnbull's emphatic view is that the Syrian president has to be brought to account.

"The crimes he has committed against his own people are so enormous and, of course now, so recent it is difficult to see how a political solution can be crafted that has him with a continuing role," Mr Turnbull told reporters at the Bomana War Cemetery on the outskirts of Port Moresby.

"If President Assad sought to have a continuing role after a political settlement, his criminal, horrendous actions - gassing his own people, women and children, babies - that surely disqualifies him from a continuing role."

Asked if he believed Assad should face court for his crimes, Mr Turnbull replied: "Those who commit war crimes should always be held accountable".

Mr Turnbull had just visited the Isurava??? memorial at the site of some of the most intense fighting 75 years ago and was clearly moved by the experience.

He described standing on a "hinge of fate" that had determined the course of the war and secured Australia and PNG's freedom from the Japanese, paying tribute to bravery, courage, mateship and endurance of those involved.

"This is a solemn place, a momentous place, a place where we should remember that sacrifice and right now, in 2017, the descendents of these men and woman are today defending Australia's freedom around the world and especially in he Middle East.

"We honour these men and women best by defending, by supporting, the soldiers, sailors, the airmen, the service men and women of the ADF today."

After receiving briefings from Defence Minister Marise Payne and the chief of the ADF, Air Chief Marshall Mark Binskin, Mr Turnbull said: "What we await now is leadership from Russia, who is the sponsor of the Syrian regime, to work with the other nations, the other powers involved in this conflict - and, of course, the United States is the greatest power connected to this conflict - to bring this shocking war to an end.

"The Assad government gave a commitment not to use chemical weapons. It said it had abandoned them. Now they have broken that commitment. There has been a swift and just response and now it is up to the Security Council, it's up to Russia in particular, to bring this conflict to an end.

"They have the leverage over the regime. If the great powers engaged in this conflict, both the global powers and the regional powers, work together, then peace can be found."