SYDNEY, Australia – Australia will shutter its embassy in Afghanistan this week, Prime Minister Scott Morrison announced Tuesday, underscoring deep fears about the "increasingly uncertain security environment" in Kabul as foreign troops withdraw.

Morrison said the facility would close as an "interim measure" on May 28 -- in three days -- "in light of the imminent international military withdrawal from Afghanistan."

The United States has formally begun withdrawing its troops from Afghanistan, opening the final chapter in America's longest-ever war, but heralding an uncertain future for a nation in the tightening grip of the Taliban.

The elected government in Kabul and Afghan security services remain weak despite two decades of foreign capacity building, and their success is far from clear without full-scale US support.

Most US troops are expected to leave by September 11, the 20th anniversary of the Al-Qaeda attacks that sparked the US-led invasion of the country.

"It is Australia's expectation that this measure will be temporary and that we will resume a permanent presence in Kabul once circumstances permit," Morrison said.

A handful of Australian troops are also leaving Afghanistan, ending a mission that cost the country billions of dollars and saw tens of thousands of military personnel deployed far from home.

Without that small contingent and the larger US force as back up, Morrison said there was an "increasingly uncertain security environment."

"The government has been advised that security arrangements could not be provided to support our ongoing diplomatic presence," he said in a statement.