The remarks, made in an interview with broadcaster BBC published on Wednesday, have incensed the Kremlin. Russian media quoted spokesman for Russian President Vladimir Putin, Dmitry Peskov, as saying the Kremlin "does not agree" with Poroshenko's statements.

He said people were overlooking more important issues, such as people dying.

"First of all, one has to understand that unfortunately, Kyiv is waging war against its own citizens," Peskov said.

In the interview, President Poroshenko said Ukraine was fighting a "real war" with the Russian state, and not simply separatists in eastern Ukraine.

He said although he did not trust Putin, he had no choice but to negotiate with him.

"I don't think that the release of my territory could happen by military means," he said.

On Tuesday Ukrainian authorities showed footage of two supposed Russian special forces members captured at the weekend in Lugansk in the separatist east.

Officials in Kyiv say that this proves Russia is backing a campaign to break up the former Soviet state, an accusation Moscow vehemently denies.

A Ukrainian Security Service spokesman said the men had been charged with involvement in "terrorist activity" and given the chance to contact family back home.

The simmering conflict has claimed more than 6,200 lives and displaced more than a million citizens.

Despite a truce being struck in February with mediation from France and Germany, clashes continue to break out, with both sides blaming each other.

Last week members of Russia's political opposition released a report claiming that more than 200 troops had died in eastern Ukraine since August.

It also said Moscow had spent more than a billion dollars (901 million euros) on fighting the conflict in the past year alone.

The document was based on research conducted by the late activist Boris Nemtsov, who was shot and killed near the Kremlin earlier this year.

Poroshenko said it wasn't just the war on Ukraine he had to worry about, but issues such as entrenched corruption.

The 49-year-old Ukrainian billionaire oligarch said he was trying to make his government as transparent as possible, because he needed "the trust of the investors, the trust of the partners, so that we can fight not only the war in the east, but one of the most important wars in my country: the war on corruption."

He said his ultimate goal would be for Ukraine to become a member of the European Union (EU) one day.

Ukraine currently has an association agreement with the EU, and has voiced intentions to apply for full membership in the future. The process usually takes years, if not decades.

an/msh (AFP, dpa)