Ukraine and the pro-Russian separatists appeared increasingly close to signing a deal to end four months of fighting, even as Ukraine's leader met Thursday with President Barack Obama and other NATO leaders in Wales.

Ukrainian President Petro Poroshenko said he's ready to order a cease-fire in the east on Friday, if a peace deal is signed at talks in Minsk, Belarus. The rebels also said they were ready to declare a truce Friday if an agreement with Ukraine is reached on a political settlement for the mostly Russian-speaking region.

Poroshenko discussed the outlines of a deal with Russian President Vladimir Putin on Wednesday, and they both voiced optimism about reaching an agreement in Minsk.

Facing major challenges with conflicts in Ukraine, Syria and Iraq and a winding down of operations in Afghanistan, NATO leaders gathered for a two-day summit at a golf resort in southern Wales. Before the official proceedings began, Poroshenko attended a meeting with Obama and the leaders of NATO's four major European powers: British Prime Minister David Cameron, French President Francois Hollande, German Chancellor Angela Merkel and Italian Prime Minister Matteo Renzi.

Later in the day, Poroshenko was to meet with the heads of state and government from all 28 NATO member states. NATO officials have made clear that membership for Ukraine isn't in the cards anytime soon, but the alliance is expected to express solid support for Poroshenko's government and announce an increase in nonlethal aid for Ukraine's military.

In Moscow, Russian Foreign Minister Sergey Lavrov warned that statements by Ukrainian officials saying that Ukraine will be seeking to join NATO were "a blatant attempt to derail all the efforts" to seek a peaceful solution to the fighting.

Pro-Russian separatists have been fighting government troops in eastern Ukraine since mid-April in a conflict that the U.N. estimates has killed nearly 2,600 people. NATO says at least 1,000 Russian fighters are helping the rebels in Ukraine.

Rebels have made substantial advances against Ukrainian forces over the past two weeks, including opening a new front along the Sea of Azov coast. That offensive has raised concerns the rebels are aiming to seize control of Mariupol, a major port of about 500,000 people, in order to secure a land corridor between Russia and Crimea, the Black Sea peninsula that Russia annexed in March.

An AP reporter saw three military-type vehicles ablaze Thursday in Berezove, a village along the main road connecting Mariupol with Donetsk, the largest rebel-held city. Rebel fighters were on the move, indicating they could be trying to take control of the strategic highway. Later, columns of smoke rose outside the nearby village of Olenivka, suggesting that Ukrainian forces were trying to retake it.

Specifics of the hoped-for peace deal are yet to be finalized. Putin has suggested that rebels halt their offensive while the Ukrainian government forces should pull back away from shelling residential areas.

Poroshenko, in his turn, called for the withdrawal of foreign troops, a diplomatic reference to Russian forces, as well as establishing a buffer zone on the border and releasing all Ukrainian prisoners held in Russia.

Both sides expressed readiness for international monitoring of the truce and prisoners' exchange.

Earlier, NATO Secretary General Anders Fogh Rasmussen accused the Russians of continued meddling in eastern Ukraine despite Putin's proclamation of a peace plan.

"What counts is what is actually happening on the ground," Rasmussen said Thursday. "And we are still witnessing, unfortunately, Russian involvement in destabilizing the situation in eastern Ukraine. So we continue to call on Russia to pull back its troops from Ukrainian borders, stop the flow of weapons and fighters into Ukraine, stop the support for armed militants in Ukraine and engage in a constructive political process."

The battles have taken a heavy toll on Ukraine's army. National Security Council spokesman, Col. Andriy Lysenko, told reporters Thursday that 837 Ukrainian servicemen have been killed and 3,044 wounded since the fighting began in April.