It comes ahead of his first visit to the United States as Prime Minister, where he'll meet with President Barack Obama and Defence Secretary Ash Carter.
Terrorism and security in the Middle East and Asia Pacific regions are expected to be key items on their agenda.
Prime Minister Malcolm Turnbull has visited Australian troops in Afghanistan a day after touring Iraq.
During his trip to Kabul, Mr Turnbull announced an extra 20 more personnel will join Australia's troop commitment to the NATO-led force supporting the Afghan central government.
The extra troops will bring Australia's total to 270.
Mr Turnbull thanked the personnel for their efforts and the credit they bring to Australia for their service in Afghanistan.
"You are making a real difference to the evolution of Afghanistan to a point where it can stand on its on two feet on maintaining its own security. The work that you are doing right across the board building capacity is absolutely critical to this country's future."
Australia's troop increase comes despite rejecting a request from United States President Barack Obama last week to commit more Australian forces to the fight against the so-called Islamic State militant group in Iraq and Syria.
Mr Turnbull says security is a global issue and technology, like smart phones, has made the world smaller and heightened terrorism.
"We say Australia is a long way from Afghanistan, and it is, I'm sure you feel it is particularly when you are missing your families. But everything is very close and very connected. So enabling Afghanistan to be safer, to be more secure, to be able to defend itself with their own people is absolutely critical to the world's security and indeed to ours."
Former Army Chief Peter Leahy says while an extra 20 troops isn't hugely significant, it's a message of Australia's commitment to Afghanistan for this year.
"The situation in Afghanistan isn't all that good at the moment. We've got a resurgent Taliban, and we've also got ISIS starting to make some moves in the area. So the security threat is significant and that presents a challenge for the government of President Ghani, which means he needs an army and he needs an army that's trained and that's out role."
Mr Turnbull spoke with a number of the 250 defence personnel involved in Afghanistan during his visit.
Peter Leahy says it's a crucial element to having troops deployed overseas.
"I think it's really important that the Prime Minister see our troops. And I thought it was fantastic the way he said thank you for your professionalism and your courage and that is really important to the troops. They know they are doing an important job and too often they are forgotten."
Meanwhile, Afghan president Ashraf Ghani has accepted an invitation from Mr Turnbull to visit Australia this year.
In a meeting with Mr Turnbull, Dr Ghani expressed his gratitude to Australia.
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