KIEV, Ukraine -- Petro Poroshenko was sworn in Saturday as the fifth president of Ukraine, promising to put an end to a separatist insurrection in the east that has divided the country for months.
The pro-European, billionaire confectioner also expressed new resolve, saying Ukraine would never accept Russia's annexation of Crimea, a point he also made in a face-to-face meeting Friday with President Vladimir Putin.
In a forceful inaugural address, Mr. Poroshenko, 48, called on rebel fighters in eastern Ukraine to put down their weapons and promised safe passage for "Russian mercenaries" who wished to return home. But he said there would be no negotiations with armed insurgents, raising the prospect of further bloodshed as the Ukrainian military seeks to quash the rebellion.
Although the United States and its Western allies expressed new hope of a diplomatic resolution after meetings with Mr. Putin in France at a commemoration of the 70th anniversary of D-Day in France, Russia's intentions in Ukraine remain unclear and there have been mixed signals on whether there is consensus among Western nations over further sanctions if diplomatic efforts fail.
Mr. Poroshenko, after being installed in a mostly solemn ceremony at the Ukrainian Parliament, said he hoped to mend relations with Russian, noting, "Citizens of Ukraine will never enjoy the beauty of peace unless we settle down our relations with Russia."
At the same time, however, he voiced no willingness to tolerate recent Russian aggression and the annexation of Crimea, which Mr. Putin has described as the righting of a historical accident that separated the peninsula from its Russian roots.
"Russia occupied Crimea, which was, is and will be Ukrainian soil," Mr. Poroshenko told an audience that included U.S. Vice President Joe Biden and other international dignitaries. "Yesterday, in the course of the meeting in Normandy, I told this to President Putin: Crimea is Ukraine soil. Period. There can be no compromise on the issues of Crimea, European choice and state structure."
Mr. Poroshenko also said that he would move swiftly to sign political and economic agreements with the European Union that Ukraine's former government, under heavy Russian pressure, backed away from in November, setting off the civil unrest in Ukraine.
"My pen is in my hands," he said, adding later, "European democracy for me is the best form of government invented by mankind."
In a sign of outreach, Russia returned its ambassador, Mikhail Zurabov, to Kiev to attend the inaugural festivities. Mr. Zurabov had been recalled to Russia after the ouster of former President Viktor Yanukovych.
And a day after President Barack Obama demanded that Russia stop the flow of weapons and fighters into Ukraine, Russian news agencies reported that Mr. Putin had ordered tighter controls on the border to prevent people from crossing illegally.
Still, violence continued to flare in the east. An assassination attempt on Denis Pushilin, a pro-Russian separatist leader in Donetsk, on Saturday resulted in the shooting death of an assistant, Maksym Petruhin.
Mr. Poroshenko won the presidency in a landslide May 25, in a special election that was called after months of civil unrest that toppled Mr. Yanukovych, who fled to Russia.
For many years, Mr. Poroshenko served in the Parliament. He was foreign minister under President Viktor Yushchenko and trade and economics minister under Mr. Yanukovych.
The new president earned his fortune making chocolate, and Russia is a major market for his company, Roshen, which has factories and other facilities there. His deep business ties in Russia and his long experience in Ukrainian politics had led to some hope that he could negotiate successfully with the Kremlin.
In his inaugural speech, however, he was resolute against Russian intervention.
"The issue of territorial integrity of Ukraine is not subject to discussion," he said. "I have just sworn 'with all my deeds to protect the sovereignty and independence of Ukraine' and I will always be faithful to this sacred promise."
The inauguration ceremony was imbued with ritual. Mr. Poroshenko swore the oath of office, with his hand on the 16th-century Peresopnytsia Gospel. He was presented with a bejeweled presidential necklace, which framed his tie of sky blue and yellow, Ukraine's national colors. He was also given the bulava, a scepter that is a historic symbol of power.
Mr. Poroshenko opened his speech by recognizing the so-called Heavenly Hundred demonstrators who were killed in clashes with the police in Kiev in the days before Mr. Yanukovych was forced from power.
"Many people thought that we got independence without any difficulty," he said. "It is not true."
After calling for a moment of silence he turned his attention to the pro-Russian violence in the east, and switched from speaking Ukrainian to Russian.
He promised amnesty for fighters who put down their weapons and safe passage for Russian insurgents who wish to go home. To the peaceful citizens of eastern Ukraine, he said he would welcome dialogue.
Mr. Poroshenko also promised a jobs program and to fight the corruption that has plagued Ukraine throughout its post-Soviet history. He said he would push for parliamentary elections later this year, aiming to meet a demand of demonstrators, many still camping out in the center of Kiev, who say that changing presidents was not sufficient.
In conjunction with Mr. Biden's visit, the White House announced $48 million in new aid to Ukraine, as well as $8 million for Moldova and $5 million for Georgia. Moldova and Georgia are also expected to sign agreements with the European Union this month and have come under Russian pressure as a result.