Russia could soon block some fruit imports from the EU and chickens from the United States, reports said Monday, as Brussels considered slapping tighter sanctions on Moscow over the Ukraine crisis.

An adviser to the chief of Russia's food and agricultural inspection service Rosselkhoznadzor said oriental fruit moths had been detected in some European imports.

The leaders of the United States, Germany, France, Britain and Italy agreed Monday on the need to impose new sanctions on Russia over its presumed role in Ukraine's insurgency, the French presidency said.

President Barack Obama, Chancellor Angela Merkel, President Francois Hollande, Prime Minister David Cameron and Prime Minister Matteo Renzi "confirmed... their intention to adopt new measures against Russia," the French presidency said after the five leaders held telephone talks.

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 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.

A fighter jet crashed in southern Russia on Sunday, killing the pilot, the head of the air force told Russian news agencies, blaming a technical fault.

"An accident took place and the pilot died," General Viktor Bondarev said, quoted by the Interfax news agency.

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.

Forensic experts have identified the first of 298 people killed in the MH17 disaster, the Dutch government said, as grieving relatives defied safety concerns to pay an emotional visit to the crash site in eastern Ukraine.

Russian President Vladimir Putin and Australian Prime Minister Tony Abbott on Saturday discussed how an international probe could be set up into the downing of Malaysian Airlines flight MH17 in Ukraine, in which 28 Australians were killed.

The two leaders held a telephone conversation "to exchange their views on aspects of organizing an independent and objective international inquiry", the Kremlin said in a statement.