KYIV, Ukraine -- Ukraine's leader said Thursday that "the most dangerous part of the war" has passed and that the conflict with pro-Russia separatists in the country's east is on the wane. Artillery fire, however, still rang out in the region's largest city.

In a news conference in Kyiv outlining a six-year plan for Ukraine, Petro Poroshenko said: "I have no doubt whatsoever that my peace plan will work and that the main and most dangerous part of the war is behind."

Poroshenko's plan includes reforming all major government agencies in the country. The president said he hoped those reforms would make the country ready for membership in the European Union by 2020.

But Poroshenko spent much of the news conference fielding questions about a conflict in the east of the country, where fighting between government and rebel forces has killed at least 3,500 people since mid-April. His peace proposal, which was laid out soon after he became president in June, were the foundation for agreements this month aimed at ending the fighting.

The first step was a ceasefire called three weeks ago that in the beginning was repeatedly violated. In recent days, reports of violations have decreased notably, although on Thursday the city council of Donetsk, the largest rebel stronghold in the region, said that artillery fire and other explosions could be heard throughout the city during the day.

Poroshenko also said he is working to arrange a meeting within the next few weeks with Russian President Vladimir Putin, but stressed it was contingent on whether the ceasefire was implemented or not.

Poroshenko, who has been at pains to justify striking a deal with the Russia-backed rebels, spent much of the news conference defending his decision to sign a peace agreement with the insurgents and said he believed Russian policy toward Ukraine had turned a corner.

"At the beginning, Russia's objective was clear," he said. "Certain people in the Kremlin administration thought Ukraine was a giant with feet of clay. They thought they could just push us, and the entire southeast of the country would dissipate."

"I would sincerely like to believe that the relation of Russia (toward Ukraine) and their plans are changing -- there has been a kind of transformation."

Ukraine and Western countries claim that Russia sent troops and equipment into eastern Ukraine to back the separatist rebels, something Russia denies.

Russia was a party to peace talks that led to a ceasefire in the region on Sept. 5. In another agreement signed Saturday, all sides agreed to remove heavy artillery from the front lines, creating a buffer zone that would help enforce the ceasefire more effectively.