As he was inaugurated as Ukraine’s new president Saturday, Petro Poroshenko proposed a cease-fire with pro-Russian separatists in the restive east and denounced a culture of corruption that has impoverished the nation.

Though he said relations with neighboring Russia must ultimately improve, he had harsh words for a country that he accused of fostering dissent by spreading propaganda.

And he vowed that Kiev would never accept Russia’s annexation of the Crimean Peninsula, declaring that “Russia occupied Crimea, which was, is and will be Ukrainian soil.”

Poroshenko’s assumption of the presidency represents a crossroads moment for this country of 45 million. Six months of upheaval have ratcheted up tensions between Russia and the West to Cold War heights, and Poroshenko’s inauguration offers a glimmer of hope to those seeking to avoid a full-blown civil war.

The billionaire candy maker known as the Chocolate King, whose election has buoyed hopes that he can pull his country out of a tailspin, lost no time in tackling some of the most urgent issues that have convulsed Ukraine.

First, he asked for a moment of silence for the protesters known as the Heavenly Hundred, who died when riot police fired on them in February. Then he proposed negotiations to resolve the conflict in the east.

At one point, he switched from the Ukrainian language to Russian, exhorting citizens to trust him instead of the pro-Russian separatists who have declared two people’s republics in the region and set up shop in government buildings.

“I don’t want war. I don’t want revenge,” he said, adding that he would not negotiate with “gunmen and other scoundrels.” He offered amnesty to those who “do not have the blood of peaceful citizens on their hands” and safe passage home for Russian nationals who have come to Ukraine to join, and in some cases lead, separatist units.

Poroshenko took office shortly after 10 a.m., arriving in the back of an ordinary black sedan with no police escort. He walked up the blue-carpeted stairs to the chambers of parliament and took his oath of office with his hand on a 16th-century illuminated Bible that is considered a national cultural treasure.

The feeling that time is running out for Ukraine permeates every conversation in Kiev.

“Nobody has the luxury of having a plan for the first 100 days. It’s the first 10 days that will be important,” said Igor Gryniv, a member of parliament who acted as a strategist for Poroshenko’s campaign.

Whether the separatists will respond to Poroshenko’s gesture was unclear, and the violence continued unabated as an aide to separatist leader Denis Pushilin was assassinated Saturday in the eastern city of Donetsk.

But Poroshenko’s words won initial praise from Russian officials. Russia’s ambassador to Kiev — who returned to the city for Poroshenko’s inauguration after a months-long absence following Viktor Yanukovych’s ouster as president — said negotiations between Russia and Ukraine could begin in “the next few days.”

“We are ready to resume dialogue,” Ambassador Mikhail Zurabov told Interfax.

Russian President Vladi­mir Putin, meanwhile, has ordered Russia’s border service to tighten border security, the Kremlin said Saturday, in an apparent attempt to slow the flow of Russian fighters to Ukraine. President Obama this week said he would strengthen sanctions if Russian citizens continued crossing the border. U.S. and European officials have accused Putin of tacitly supporting an insurgency in the east while making conciliatory moves toward the new leadership in Kiev.

Poroshenko said a peaceful resolution to the war is a necessary foundation for political and economic progress, and he called for early elections in parliament and the eastern provinces. He said he would seek full membership in the European Union and sign an agreement that would allow Ukrainians to travel visa-free throughout the union.

“We are turning back to Europe,” he said. “This path is irreversible.”

Poroshenko admonished a culture of corruption that has impoverished the nation and urged Ukrainians to buck the everyday practice of paying bribes to government officials high and low.

“We need an anti-corruption pact between the government and the people,” he said. “Bureaucrats do not take bribes, and people do not give bribes. We will not be able to change the country unless we change ourselves.”

Acknowledging that corruption has worked its way into the armed forces battling the insurgents, he said he aimed to rebuild the military into an elite fighting force.

“The word general must become identified not with the word corruption, but with the word hero,” he said.

In speaking bluntly to his compatriots, Poroshenko, 48, reflected the national sense of urgency that propelled him into office. He was the first president to win a majority in every region of the country since Ukraine became independent of the Soviet Union in 1991.

“He won’t have a honeymoon,” said Oleh Rybachuk, chairman of the Center of United Actions, a Ukrainian advocacy group focused on government accountability. “He won’t have a honey week. Maybe, if he’s lucky, he’ll have a honey day.”

Gryniv said Ukrainians are feeling emboldened by the success of the protests that led to the ouster of the previous president, Yanukovych, in February.

“They believe in themselves now,” Gryniv said. “Poroshenko recognizes that he will lead a country that wants to control him. At the first mistake, there could be an explosion.”

That sentiment could constrain Poroshenko. Many Ukrainians, who blame Russia for the unrest, do not favor negotiating anything with their neighbor, said Andriy Meleshevych, dean of the law school at Mohyla Academy, one of Ukraine’s premier universities.

“If he doesn’t want protests on the streets of Kiev, he won’t do that,” he said.

But many in the east have pressed for talks as residents flee their homes to escape life in a combat zone that grows more dangerous by the day.

In Donetsk, the capital of one of two breakaway republics declared by the rebels, Ukrainian troops are massed across the region and rebels occupy government buildings in more than a dozen towns and cities. Many worry that Poroshenko will initiate a government offensive and cause heavy civilian casualties.

“He needs to stop the war,” said Oksana Siemenova, 27, who gave up her job at a bank after insurgents set up a base next door. “He should negotiate with these people, because otherwise the real war begins.”

Some Ukrainians say Poroshenko, who in a burst of hyperbole once vowed to crush the separatists in “hours, not months,” should root out corruption to build support for peace, not the other way around.

Corruption is pervasive in Ukraine at every level of government. Civilian groups have called for a purge of officials tainted by their ties to old regimes — not only politicians, but also judges and police officers.

“Poroshenko has a credit slip from the people, and he has to pay it as soon as possible,” said Svitlana Zalishchuk, a former journalist who has protested and lobbied for governmental reforms. “He’s one of the oligarchs. He was supported by the very rich, and now he has to impose some rules. We want real changes that show he’s different.”

To that end, Poroshenko, considered the sixth wealthiest man in Ukraine, has promised to sell most of his $1.3 billion business empire and focus on governing. Besides chocolate factories, he owns an insurance company, an investment bank and shipyards. But he has steadfastly refused to unload his news network, an asset he could use to build popular support.

On the still-gritty streets of the Maidan, the epicenter of the anti-government protest movement, activists still live in tents and tourists light candles at makeshift shrines to dead protesters. But several people there said they believed Poroshenko would be different from previous leaders.

“I trust him to find a compromise with Russia. But if he lies to us, people will be really disappointed,” said Oksana Petrulyak, an elementary school teacher who was ushering her 13-year-old son past an array of photos of fallen protesters.

Petrulyak said she was discussing politics recently with a friend who opined that Ukraine has had the government it deserves.

“No,” she said with anger, “we’re a hardworking, intelligent people. It’s shameful what we’ve gone through. Pity our people.”

Witte reported from Donetsk. Michael Birnbaum in Moscow and Alex Ryabchyn in Kiev contributed to this report.