Russian President Vladimir Putin on Wednesday emerged from a Moscow church and told journalists he had lit a candle in memory of those who died defending separatist eastern Ukraine.

"Who did I light a candle for? For those who were injured and those who gave their lives defending people in Novorossiya," Putin said, shown on Russian television.

House Speaker John Boehner announced Wednesday he will invite Ukraine's President Petro Poroshenko to address a rare joint meeting of the U.S. Congress on September 18.

"Having President Poroshenko address Congress is another signal of our steadfast commitment to the aspirations of his people," Boehner said in a statement.

At the last checkpoint before the airport in Ukraine's main insurgent bastion of Donetsk, separatist fighters manning the barricades are dismissive of suggestions that the ceasefire is holding.

"Here's your ceasefire," scoffed Dmitry, pointing to the fin from an exploded mortar round, lined up with another three against a wall at the Putilovskiy Bridge checkpoint to the north of the city.

Crimea's Kremlin-loyal leader on Wednesday said that if the world recognizes an independent Scotland, then it should also offer similar recognition to the Black Sea peninsula which has joined Russia.

Acting regional head Sergei Aksyonov said that the West would have "no other option" but to back Crimea's move to break away from Ukraine, if it also accepts a Scottish vote to split from the United Kingdom.

President Vladimir Putin on Wednesday accused Western countries of creating the Ukrainian crisis and using it to revive NATO.

Speaking after the Western military bloc agreed to boost its presence in eastern Europe, the Russian strongman warned Brussels and Washington against "any hysterics" if Russia chooses to retaliate.

Amnesty International on Wednesday called on Russia to urgently investigate allegations of war crimes in Ukraine and free two prisoners it said were illegally taken across the border.

"We are calling on the Russian government to immediately hand over two of the prisoners they are holding from Ukraine in Russia," Amnesty chief Salil Shetty told journalists in Moscow.

A majority of Europeans and Americans want their governments to support Ukraine, even if that means a risk of greater conflict with Russia, a survey suggested on Wednesday.

In its annual survey of public opinion in 13 major countries, the German Marshall Fund of the United States think tank found that the Ukraine crisis had entrenched mutual suspicion between Russia and the West.

Ukrainian President Petro Poroshenko said Wednesday that Russia had withdrawn most of the troops it allegedly snuck across the border to bolster pro-Kremlin rebels, and vowed greater autonomy for the separatist east in order to sustain a fragile new truce.

The pro-Western leader's comments came just as EU envoys were gathering in Brussels to debate a new wave of sanctions aimed at punishing Russia for its perceived attempts to break up the ex-Soviet state.

Tehran said Tuesday it would enhance energy cooperation with Russia but there would be no imminent oil-for-goods deal of the kind that has raised concerns in Washington.

"Iran and Russia have agreed to cooperate in the energy field," Ali Majedi, Iran's deputy oil minister, told the ISNA news agency.

Pro-Russian rebels in east Ukraine said on Tuesday they did not have the capability to shoot down Malaysia Airlines flight MH17, after Dutch investigators said it was hit by numerous "high-energy objects".

"I can say only one thing: we simply do not have the military hardware capable of shooting down a Boeing passenger jet such as the Malaysian plane," Alexander Zakharchenko, prime minister of the self-proclaimed Donetsk People's Republic, told Russia's Interfax news agency.