U.S. President Barack Obama insisted Monday that the sanctions Western powers imposed on Moscow in the wake of Russia's intervention in Ukraine were meant to protect Kiev's sovereignty not trigger conflict with Moscow.

"We cannot stand by when the sovereignty and territorial integrity of a nation is flagrantly violated," he said, addressing the United Nations General Assembly.

A Ukrainian soldier was killed and another was wounded in a landmine blast in the rebel-held east, where a ceasefire has been holding for almost a month, a defense official said Sunday.

"Yesterday near Gorlivka, one Ukrainian soldier was killed and one injured. It was a result of a mine explosion," military spokesman Oleksandr Motuzyanyk told journalists, referring to a city about 30 kilometers (18 miles) from the rebels' de facto capital Donetsk.

Russia agreed to resume gas supplies to Ukraine over the winter under a deal clinched late Friday with the European Union, capping months of difficult talks overshadowed by the Ukrainian conflict.

European Commission vice president for energy, Maros Sefcovic, told a press conference the preliminary deal was a "crucial step" to ensure Ukraine has gas supplies from October through March and that Europe receives onward deliveries. 

Ukraine's pro-Russian rebels in the separatist Lugansk region on Thursday banned 10 Western health relief groups for "grave violations" of local laws.

The list includes such world-renowned organizations as Doctors Without Borders (MSF) and the Czech Republic's People in Need (PIN).

Russia, Ukraine and the European Union are set to resume gas talks in Brussels on Friday aimed at restoring Russian gas supplies to neighboring Ukraine, the Russian energy minister said Thursday.

The spokeswoman of energy minister Alexander Novak told AFP "we confirm" the meeting is going ahead.

Ukraine's pro-Moscow insurgents showed off their military prowess on Thursday by launching exercises involving heavy tanks that Kiev claims they had covertly received from Russia.

The self-proclaimed "tank biathlon" mirrored maneuvers that Russia has been staging with its former Soviet allies since 2013.

NATO head Jens Stoltenberg told Agence France Presse Thursday there was still a "strong" Russian presence in eastern Ukraine in support of pro-Moscow rebels although a recent ceasefire seems to be holding.

Stoltenberg said he backed the continuation of European Union and United States sanctions against Russia over its involvement in Ukraine until Moscow changes its behavior.

French President Francois Hollande said Wednesday Egypt had agreed to buy two Mistral warships which France built for Russia before scrapping the sale over the Ukraine crisis.

The deal is the second big military contract this year between France and Egypt, which Hollande said he increasingly views as a strategic partner.

Ukrainian airforce helicopter pilot Nadiya Savchenko on Tuesday blasted Russian prosecution 'lies' against her at the start of a trial over the murder of two journalists that has caused outrage in Kiev and the West. 

Savchenko faces up to 25 years in prison for her alleged role in the deaths of two Russian reporters killed by mortar fire last summer in eastern Ukraine.

Germany on Monday criticized local elections being organized by pro-Moscow separatists in eastern Ukraine as a breach of a February peace deal and urged Russia to distance itself from the idea.

"We consider with great concern the announcement by pro-Russian separatists of the organization of elections, so-called municipal elections," said Chancellor Angela Merkel's spokesman Steffen Seibert.