Russia said Monday that observers from the Organization for Security and Cooperation in Europe (OSCE) would be deployed at its border checkpoints with rebel-controlled eastern Ukraine in the next few days.

Russian Foreign Minister Sergei Lavrov said that OSCE monitors would see that Russia is not sending arms and fighters to help the rebels.

Black boxes recovered from downed Malaysia Airlines flight MH17 in rebel-held east Ukraine show shrapnel from a rocket explosion caused the passenger jet to crash, a Ukrainian security official said Monday.

International investigators "indicated that data from flight recorders show that the reason for the destruction and crash of the plane was massive explosive decompression arising from multiple shrapnel perforations from a rocket explosion," Andriy Lysenko, spokesman for Ukraine's National Security and Defense Council, said.

Dutch and Australian forensic investigators on their way to the MH17 crash site turned back Monday after "explosions" in the area, a government spokeswoman in The Hague said.

"They have returned in the direction of Donetsk," justice ministry spokeswoman Sentina van der Meer told Agence France Presse. "Explosions were heard, and they were warned by the locals."

The downing of Malaysia Airlines flight MH17 "may amount to a war crime,” the U.N. said Monday, adding that fighting in east Ukraine has claimed over 1,100 lives with both government and rebel forces using heavy weaponry in built-up areas.

U.N. High Commissioner for Human Rights Navi Pillay condemned the "horrendous shooting down" of the Malaysian passenger jet in rebel-held territory that killed all 298 people on board, and demanded a "thorough, effective, independent and impartial investigation".

The United States on Sunday released satellite images to bolster its claim that Russian artillery has fired across the border into Ukraine, targeting government forces in support of separatist rebels.

The four images, prepared by the office of the Director of National Intelligence and forwarded to reporters by the State Department, show sections of the Russia-Ukraine frontier.

Downed flight MH17 has claimed another victim in a 93-year-old man who succumbed to the "indescribable grief" of losing his daughter, son-in-law and two grandchildren in the crash, family have said.

Hendrik (Henk) Palm, from the northern Dutch town of Roden, died "after the indescribable grief of losing his daughter, Erla (Palm), son-in-law Rob (van der Linde) and grandchildren Merel and Mark" in the Malaysia Airlines crash, family members said in a death notice carried by De Stentor regional newspaper.

Thirteen people including two children were killed Sunday in fierce clashes in the key insurgent holdout of Gorlivka in east Ukraine where government troops are battling rebel fighters, local authorities said.

"As a result of military actions in Gorlivka 13 people have died, among them two children of one and five," the Donetsk regional administration said in a statement, adding that operations by medical teams in the crucial insurgent base, a city of some 250,000 around 45 kilometers north of Donetsk, were hampered by "constant shooting."

Pope Francis called Sunday on warring parties in the Middle East, Iraq and Ukraine to put an end to violence which is wounding and killing countless children.

"Stop, please stop! I beg you with all my heart," the 77-year-old Argentine pontiff pleaded before pilgrims packed in St. Peter's Square for the weekly Angelus prayer.

Heavy shelling around the crash site of downed Malaysian flight MH17 forced Dutch and Australian police to scrap a planned visit as they sought to secure the scene 10 days after the disaster.

Any airline would struggle with the devastating impact of losing one jet full of passengers, especially if it had already been bleeding money for years.

But losing another just months later is pushing crisis-hit Malaysia Airlines to the brink of financial collapse, airline experts said, spotlighting whether it can steer its way out of extended turmoil as once-troubled carriers such as Korean Air and Garuda Indonesia did before.