BEIJING, July 19 -- As international investigators have begun arriving at the crash site of Malaysia Airlines Flight 17, world leaders demanded a thorough and transparent investigation while offering their condolences to the families of the victims.

The Boeing 777-200, en route from Amsterdam to Kuala Lumpur, went down Thursday in eastern Ukraine, killing all the 298 passengers and crew aboard, according to Malaysian Airlines.

Chinese President Xi Jinping on Friday said he was "shocked" at the incident and called for a "fair and objective" probe into the crash.

The Chinese president also conveyed his deep condolences on the massive loss of lives and sincere sympathies with the families of the victims.

Dutch Prime Minister Mark Rutte said his country, which lost 173 nationals in the crash, would not rest until the perpetrators of the possible attack on the crashed plane are detected, adding that his country have already sent its Safety Board to Ukraine to support an international investigation.

The Dutch government advocates that an independent investigation team should clarify all questions regarding the incident.

Russian President Vladimir Putin on Friday demanded a thorough and unbiased investigation into the crash, and said the findings must be revealed to the world.

He also called for a peaceful settlement of the Ukraine crisis as soon as possible, saying that he hoped Ukrainian President Petro Poroshenko would agree to a ceasefire to allow the investigation team to enter the site.

In an address at the White House on Friday, U.S. President Obama said the downing of the airliner would be a "wake-up call" for Europe and the world that an escalation of the conflict in eastern Ukraine has consequences.

The United States is prepared to offer immediate assistance for a "prompt, full, credible, and unimpeded" international investigation into the Malaysian airliner crash, Obama said.

Malaysian Prime Minister Najib Razak said they must and will find out precisely what happened to this flight, adding that "if it transpires that the plane was indeed shot down, we insist that the perpetrators must swiftly be brought to justice."

Najib said they had established emergency operations centers, and Malaysian officials had been in constant contact with their counterparts in Ukraine and elsewhere.

Australian Prime Minister Tony Abbott described as a "terrible tragedy" the crash of MH17 that has claimed the lives of as many as 27 Australians.

It would be an "unspeakable crime" if the plane was shot down, said Abbot, adding that the perpetrators should swiftly be brought to justice.

UN Secretary-General Ban Ki-moon on Friday strongly condemned the downing of MH17.

"This horrifying incident must at the very least prompt a serious and sustained effort to end the fighting in Ukraine," said a statement issued by Ban's spokesperson.

Ban called for a "full and transparent international investigation" into the incident and offered the full cooperation of the world organization in such an inquiry.

"There must be accountability for this tragedy: anyone found to be responsible must be brought to justice," Ban noted in the statement.

The UN chief called on all parties to give investigators immediate and unfettered access to the crash site, and also conveyed his deepest condolences to the families of all victims and to the governments and peoples of their countries of origin.

Other countries, including Britain, France, Singapore, New Zealand, Indonesia, Iran, Estonia, Chile, Cuba, Switzerland, Iceland and Belgium, have also either conveyed their condolences or called for an independent and fair probe into the incident.