Prime Minister Arseny Yatseniuk said only membership of NATO would enable Ukraine to defend itself from external aggression.
Kiev and its Western backers accuse Moscow of sending troops and tanks into eastern Ukraine in support of pro-Russian separatists battling Ukrainian forces in a conflict that has killed more than 3,000 people. Russia denies the accusations.
A ceasefire negotiated by envoys from Ukraine, Russia, the separatists and Europe's OSCE security watchdog, has been in place in eastern Ukraine since Sept. 5 and is broadly holding despite regular but sporadic violations, especially in key flashpoints such as Donetsk.
On Saturday afternoon, a Reuters reporter heard heavy artillery fire in northern districts of Donetsk, the largest city of the region with a pre-war population of about one million. He saw plumes of black smoke above the airport, which  is in government hands. The city is controlled by the rebels.
Speaking at a conference in Kiev attended by Ukrainian and European lawmakers and business leaders on Saturday, Yatseniuk made clear he did not view the ceasefire as the start of a sustainable peace process because of Putin's ambitions.
"We are still in a stage of war and the key aggressor is the Russian Federation ... Putin wants another frozen conflict (in eastern Ukraine)," said Yatseniuk, a longtime fierce critic of Moscow and a supporter of Ukraine's eventual NATO membership.
Yatseniuk said Putin would not be content only with Crimea - annexed by Moscow in March - and with Ukraine's mainly Russian-speaking eastern region.
"His goal is to take all of Ukraine ... Russia is a threat to the global order and to the security of the whole of Europe."
Ukrainian military spokesman Andriy Lysenko told a daily briefing that one soldier and 12 rebels had been killed in the past 24 hours, without specifying where they had died. That would bring the death toll among Ukrainian forces since the start of the ceasefire eight days ago to six.
The rebels have not said how many of their men have died in the same period.
Government forces still hold Donetsk airport, while the city is in separatist hands.
Putin says Russia has the right to defend its ethnic kin beyond its borders, though Moscow denies arming the rebels and helped broker the current ceasefire with Kiev.
Asked about future NATO membership, a red line for Russia, Yatseniuk said he realised the alliance was not ready now to admit Kiev, but added: "NATO in these particular circumstances is the only vehicle to protect Ukraine."

Latest News from World News Desk