It is, in the words of one frustrated official, "one of the biggest open crime scenes in the world."

And yet, 11 days after Malaysia Airlines Flight 17 was blown out of the sky by a suspected surface-to-air missile, the Dutch investigators in charge of finding out what happened have yet to lay eyes on the wreckage or the human remains believed to remain strewn across the enormous debris field.

The latest setback came Monday, when a 45-person team of Dutch and Australian experts, accompanied by monitors from the Organization for Security and Co-operation in Europe, abandoned their effort to reach the site after hearing explosions and being warned of heavy fighting in the area.

It's the same thing that happened Sunday.

"We're really sick and tired of being delayed," Organization for Security and Co-operation in Europe spokesman Michael Bociurkiw told CNN's "New Day."

"We all know there are still human remains out there exposed to the elements, number one," he said. "Secondly, it is one of the biggest open crime scenes in the world as we speak, and it is not secured. There's no security perimeter around the 30- or 35-square-kilometer site."

According to unconfirmed reports from pro-Russian rebels,Ukraine's military broke through to part of the crash site Monday and had stationed armored personnel carriers and dug trenches there.

"Safe work of experts and observers is impossible," Vladimir Antyufeev, the acting Prime Minister for the self-proclaimed Donetsk People's Republic, said Monday.

The United Nations and other countries have repeatedly called for a cease-fire to allow investigators a safe working environment at the crash site, which the U.N. human rights chief said Monday could be the scene of a war crime.

The Malaysian government had struck a deal with rebels to allow unarmed international police officers to guard the site, but the fighting has made that impossible.

"This is a contested zone. There is active fighting going on," Andrew Colvin, deputy commissioner of the Australian Federal Police, said at a news conference Monday in Canberra.

"We are working on the basis that if it's a permissive environment, we will go in," he said.

Bociurkiw said Monday that investigators will try to reach the site again Tuesday.

"We will keep trying every day," he said.

A CNN crew joined the convoy that attempted to go to the crash site Monday, but the media were stopped by armed men near Shakhtorsk. The forensic teams turned around not long later.

Other people were also fleeing the violence.

One man said jets were flying over his home.

"My little one is terrified," the man said.

As of Monday, 227 coffins bearing remains from the crashed plane had been sent to the Netherlands, where forensic investigators were working to identify them.

Of the 298 people killed in the crash, 193 were Dutch, 43 were Malaysian, and 27 were Australian.

More than 200 forensics experts from all over the world are working at a Dutch military base to identify the remains, according to Howard Day, who is leading the effort.

Investigators aren't sure how many sets of remains they have. Only one victim -- a Dutch man -- has been identified.

"This will take weeks; it will take months," Day said.

Experts are using a variety of approaches in their work, including dental records, DNA analysis and fingerprints, he said.

"We don't just identify people from a photograph or from an item of property that may be on them, because there's been countless mistakes, examples of mistakes where that's happened in the past over the years, even small incidents, like car crashes," he said

(CNN)