"The Vietnamese Government has advised the Australian Government that it will not permit the ceremony to commemorate Vietnam Veteran's Day at the Long Tan cross site at 3:30pm on August 18 to proceed," DFAT said in a statement.

"An official party, including the Australian and New Zealand ambassadors, will lay a wreath and we understand small groups will still have access to the site on the day.

"The Government is deeply disappointed at this decision, and the manner in which it was taken, so close to the commemoration service taking place."

The news came after Vietnamese police blocked access to the Long Tan memorial site, as local officials discussed whether to allow a planned event to go ahead tomorrow.

An ABC crew was stopped about 200 metres before the site's memorial cross.

No clear reason was given for blocking access to the site, which is on a private farm, but access to the cross was open on Tuesday.

Australia had been working closely with Vietnamese authorities for 18 months to prepare for the event, the DFAT statement said.

"We have gone out of our way to make sure that this was going to be a low-key commemoration," Veterans' Affairs Minister Dan Tehan, said at a press conference.

Memorial events have been held at Long Tan since 1989.

"We understand that there are sensitivities still in Vietnam," Mr Tehan said, adding "deep sensitivities" surrounding the Battle of Long Tan were cited as the reason for the decision.

"But one of the bitterly, bitterly disappointing things about what has occurred is the fact that this decision has taken place with such short notice."

For many veterans, this would have been their first visit to Vietnam since the war.

By Liam Cochrane - Australian Brodcasting Corporation News - August 17, 2016

Vietnam War: Veterans hope for answers from former enemy in return to Long Tan

Men who fought in the Battle of Long Tan hope a face-to-face meeting with members of the Viet Cong will help to bring closure, half a century after the bloody battle.

It has been 50 years, but Bill Akell still has vivid flashbacks of bodies and dismembered remains lying in the mud the day after the deadly battle at Long Tan.

"One of the thoughts that will always remain with me is … a young kid, a dead Viet Cong fighter, I reckon he was about 16 or 17 years old, and he was propped up against a rubber tree and it looked as though his eyes were looking at my eyes," Mr Akell says.

"The horrible thing about it was that there was no bottom half."

The 108 members of D Company were ill-equipped and outnumbered at least 10-to-1 in the battle near Australia's taskforce base at Nui Dat.

Until reinforcements arrived three hours later their fate appeared to be sealed.

When the intense fighting ended, 18 Australian soldiers and an estimated 245 members of the Viet Cong were dead.

A 19-year-old private, Mr Akell was one of the Australian soldiers sent back onto the battleground to count the dead.

"You had to be as accurate as possible," he says.

"That was really a matter of looking at bits and bits, that to me looked as though it's one body, so you gather up all the pieces and put it in the hole."

The final enemy death toll is one of several uncertainties veterans hope to clear up after all these years.

Unanswered questions remain

Mr Akell along with about a dozen of his comrades are hoping that returning to the battleground 50 years on will help answer some of their long-awaited questions.

Had they walked into an ambush?

Did the Viet Cong have more men on the other side of the taskforce waiting?

Had they removed bodies before Australian soldiers counted the dead?

Long Tan platoon commander Dave Sabben says veterans have scheduled private meetings with members of the former enemy.

"We'd like some answers," he says.

"How many people did they have? What were their intentions?

"We hope to meet some of the enemy commanders.

"We hope after 50 years they will break down their natural secrecy and privacy and open up to us."

But given senior commanders would now most likely be in their 80s or 90s, they have also come to terms with the fact that this may not be possible.

'Long Tan lives with you for the rest of your life'

This is not the first time Mr Sabben and Mr Akell have returned to Vietnam.

Based on Mr Akell's dark experience during his visit to the Long Tan cross memorial this time 10 years ago, he is prepared for another emotional journey.

"I just wanted to wander into the rubber tree plantation by myself and have a couple of minutes with my own thoughts," he says.

"It was like there was a glass wall in front of me. My body wouldn't let me.

"I started to shake and tears were just running down my face. I nearly collapsed."

The welts on Mr Akell's skin which he believes were caused by Agent Orange — the toxic chemicals US forces dumped on South Vietnam's jungles — are a daily reminder of the Vietnam War.

Even if this trip does help to bring some closure, the 69-year-old is well aware that the painful memories will never fade.

"Long Tan lives with you for the rest of your life."

By By Margaret Burin - Australian Brodcasting Corporation News - August 17, 2016