Australia’s foreign minister says Vietnam has withdrawn permission for a ceremony to commemorate the 50th anniversary of Australians’ most costly battle of the Vietnam War.

More than 1,000 Australian veterans and their families have traveled to Vietnam to commemorate the anniversary of the Battle of Long Tan at a cross marking the site where 18 Australian soldiers and hundreds of North Vietnamese and Viet Cong troops died on Aug. 18, 1966.

Foreign Minister Julie Bishop said Wednesday that the Vietnamese government had advised it will not permit the afternoon ceremony to proceed.

She says an official party including the Australian and New Zealand ambassadors will lay a wreath Thursday and small groups will have access to the site on the day.

The anniversary has become Australia’s official Vietnam Veterans Day.