Secretary-General Ban Ki-moon is calling for an immediate halt to hostilities around the crash site of Malaysia Airlines Flight 17 in eastern Ukraine to allow unimpeded access for international investigators.

U.N. spokesman Stephane Dujarric said Wednesday Ban "is deeply disturbed" that investigators and forensic teams have been unable to go to the site because of heavy fighting in the area.

"The secretary-general recalls that there are victims' remains yet to be found and that key pieces of evidence remain at the site," Dujarric said. "The families of the victims of this horrific tragedy deserve closure and the world demands answers -- international teams must be allowed to conduct their work."

A Security Council resolution demands that armed groups in control of the crash site end hostilities to enable an investigation.