Ukrainian President Petro Poroshenko repeated Friday there could be no military solution to the crisis engulfing eastern Ukraine and said new sanctions against Russia imposed by the United States and the European Union reflect Western solidarity with his country.

Poroshenko also announced that his government had exchanged dozens of prisoners in an overnight swap with pro-Russian separatists as part of the shaky cease-fire deal that went into effect a week ago.

The twin messages reflect the contrasting objectives for Ukraine’s leaders: Trying to keep the cease-fire intact while also endorsing measures that are likely to anger the separatists and their backers in Moscow.

As a next step, Poroshenko said he hoped for progress next week toward a pact for closer ties with the European Union — a move that helped touch off the conflict this spring.

“There is no military solution for this crisis,” Poroshenko told E.U. and Ukrainian lawmakers and businessmen at a conference in Kiev.

He noted that greater autonomy could be offered to rebel-held areas in a bid “to keep the country united.’’ But he insisted that security and foreign policy must stay in the hands of the central government.

The conference — the annual Yalta European Strategy Conference — was held in Kiev rather than Yalta, a city located in Crimea. Moscow annexed the Ukrainian autonomous region in March after pro-Russian separatists backed by Russian troops seized control of the peninsula and staged an independence referendum. Russian-backed separatists in eastern Ukraine followed suit in April, triggering a five-month-old conflict that has claimed the lives of almost 3,000 people.

The prisoner exchange took place under the cover of darkness outside the rebel-held city of Donetsk in embattled eastern Ukraine.

Poroshenko said 36 Ukrainian servicemen were released in exchange for 31 pro-Russian separatists. He said 21 soldiers were freed Thursday.

Rebels returned 700 Ukrainian prisoners earlier this week in the first swap under the cease-fire deal reached during recent talks in Minsk, Belarus. Hundreds of prisoners are believed to be held by each side, although no figures have been released.

Isolated Cease-fire violations flare frequently, but both sides maintain that the truce is generally holding. Shortly after Friday’s prisoner exchange, rocket fire was heard from central Donetsk, according to the Associated Press.

“There is an ongoing process of talks,” Yuriy Tandit, a negotiator for the government, told the AP amid the prisoner exchange. “We are meeting each other’s demands and fulfilling our promises.”

Meanwhile, expanded sanctions by the United States and the European Union took effect. They seek to ratcheting up pressure against Moscow for its involvement in the Ukraine crisis.

The sanctions take aim at Russia’s energy sector and further constrict the country’s vital financial and defense industries’ access to global markets and resources.

They strengthen measures that the United States and the E.U. instituted in late July to target key engines of the Russian economy after the downing of Malaysia Airlines Flight 17 over eastern Ukraine. The Boeing 777, carrying 298 passengers and crew, was shot down by a Russian-supplied surface-to-air missile system from rebel-held territory in eastern Ukraine, U.S. and Ukrainian officials said.

In further tensions between the West and Russia, nine European nation demanded that Moscow immediately release an Estonian security service officer abducted by unknown gunmen Sept. 5 and taken across the Russian border.

The officer, Eston Kohver, is being held in Moscow and defense lawyers believe he will be charged with espionage, the AP reported. Russia claims he was detained on its territory.

President Obama visited Estonia last week and pledged NATO would assist Baltic states against any possible Russian aggression.

Deane reported from Rome.