Former U.S. presidential contender and outspoken Kremlin critic John McCain warned on Thursday that Western allies risked leaving behind a "landlocked Ukraine" unless they provided Kiev with weapons to fend off Russia.

The Republican senator alleged that Russian President Vladimir Putin had pushed 4,000 troops and a vast quantity of tanks across the border to help separatist fighters in Ukraine establish a land-link with the Crimea peninsula which Moscow seized from Kiev in March.

Ukrainian President Petro Poroshenko announced that a ceasefire plan aimed at halting five months of conflict in the industrial east would be signed on Friday.

His comments, on the sidelines of a NATO summit largely devoted to the crisis in Ukraine, followed talks on a peace blueprint between Poroshenko and Russian President Vladimir Putin on Wednesday.

Ukraine on Thursday raised hopes of a ceasefire with pro-Moscow rebels during a NATO summit where Britain and the United States urged the international community to stand up to Russia and counter the threat from Islamic State.

President Petro Poroshenko briefed leaders, including U.S. President Barack Obama and German Chancellor Angela Merkel, and said he expected a deal to be signed on Friday "for the gradual introduction of the Ukrainian peace plan."

France may have frozen the delivery of the controversial "Mistral-class" helicopter gunship to Russia, but its construction is still ongoing, a well-informed source said on Thursday.

Dutch air crash investigators have announced that they will release a preliminary report next Tuesday into what brought down flight MH17 over east Ukraine, killing 298 passengers.

Veteran U.S. diplomats who have tussled with some of the globe's greatest foreign policy challenges warned Wednesday that in a turbulent world American diplomacy remains essential for peace and stability.

Germany's foreign minister on Wednesday saw a tentative "sign of hope" after a ceasefire announcement by Ukraine but warned that Kiev, and especially Moscow, needed to show they meant it.

Frank-Walter Steinmeier said reports of talks between the Ukrainian and Russian presidents and "cautious" discussion of a ceasefire "is perhaps a small sign of hope" but that the next few days would reveal if it signified more.

Russian President Vladimir Putin on Wednesday called on both Ukrainian rebels and government forces to cease fire and agree to the broad terms of a truce ending their four-month war.

Putin's first direct appeal on the insurgents to lay down their weapons came hours after the beleaguered Ukrainian president, Petro Poroshenko, said he and Putin had agreed on a ceasefire deal.

At least 87 Ukrainian soldiers were killed after being surrounded by pro-Russian rebels in the eastern town of Ilovaysk, a top local official said on Wednesday.

The deputy army recruiting commander of Ukraine's southeastern Zaporizhia region, which has not been affected by the fighting, said the soldiers' bodies had been delivered to a local morgue in the past two days.

When Russian paratrooper Nikolai Kozlov was deployed to Crimea to help Moscow take over the peninsula from Ukraine, his parents were proud of him.

Six months later Kozlov is disabled for life, an amputee now recovering in hospital from wounds incurred on a Kremlin-orchestrated covert mission to Ukraine to prop up separatists fighting against Kiev.