The leaders gathered at a summit of the Western military alliance in Newport, Wales agreed to set up new funds to help Ukraine's military effort and treat wounded soldiers in a five-month conflict in which more than 2600 people have died.
European and US officials at the talks said they were ready to approve fresh economic sanctions on Russia on Friday, although implementation could be delayed pending ceasefire talks scheduled for the same day.
NATO leaders on Friday are also expected to approve plans to position troops and military equipment in Eastern Europe to reassure ex-Soviet bloc member states unnerved by Russia's actions.
"While talking about peace, Russia has not made one single step to make peace as possible," NATO chief Anders Fogh Rasmussen said after Ukraine-focussed talks at the leaders' summit.
"Instead of de-escalating the crisis, Russia has only deepened it," he said, adding that previous Russian statements on peace had been "a smokescreen for continued Russian destabilisation of the situation".
But Rasmussen left open the door to a seven-point peace plan put forward on Wednesday by Russian President Vladimir Putin, saying: "If we are witnessing genuine efforts for a political solution, I would welcome it".
Poroshenko said he was hopeful about the plan because the initiative had come from pro-Moscow rebel leaders in eastern Ukraine.
But he added that political negotiations would be a "tough challenge", warning that Ukraine's independence and territorial integrity were "not for negotiation".
Poroshenko said some NATO members would cooperate with Ukraine on "non-lethal and lethal military items" although he did not specify which countries were involved and whether it would include direct arms supplies.
Poroshenko earlier briefed a group of NATO leaders, including British Prime Minister David Cameron, US President Barack Obama, French President Francois Hollande and German Chancellor Angela Merkel.
Hollande called for a "real ceasefire" that would lead to a broader political agreement, and said France would only deliver warships worth 1.2 billion euros ($A1.8 billion) to Russia in November if these conditions were in place.
"If actions follow words remains to be seen tomorrow or in the coming days," Merkel said on the sidelines of the summit.
AFP reporters on Thursday heard explosions on the outskirts of the flashpoint city of Mariupol and renewed shelling and gunfire in the rebel stronghold of Donetsk.
Russian Foreign Minister Sergei Lavrov also lashed out, denying Russian involvement and accusing the US of undermining peace efforts by supporting "a pro-war party" in Kiev.
The 28 NATO leaders must also tackle the menace of Islamist extremists in Iraq and Syria.
Cameron and Obama said in an editorial in the Times that they would not be "cowed" following the beheading of two US journalists by Islamic State (IS) jihadists and promised to "confront" the radicals.
There were reports of fresh brutality on that front.
Police and witnesses said IS kidnapped dozens of residents of a village in Kirkuk province after locals there burned one of its positions along with a jihadist flag.
Rasmussen said NATO would "seriously" examine any request from Iraq for help in its campaign against the Islamic State, while Cameron said Britain was actively considering arming the Kurds.
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