Ukraine's new president has called for a dialogue with representatives of the country's east that has been swept by a separatist insurgency, but insisted he will still not talk with rebels, who he described as "gangsters and killers".
In a combative inaugural speech on Saturday, Petro Poroshenko also vowed that Ukraine would not give up Crimea, the Black Sea peninsula that Russia annexed from it in March.
"Crimea was, is, and will be Ukrainian," Poroshenko said after his swearing-in .
His speech drew an ovation from guests at a ceremony attended by Lithuanian President Dalia Grybauskaite, US Vice President Joe Biden and senior EU officials.
He stressed the unity of Ukraine, which is fighting a pro-Russian separatist uprising in the east, and said it would not become a federalised state as advocated by Moscow.
Poroshenko, 48, also said he intended very soon to sign the economic part of an association agreement with the European Union, as a first step towards full membership.
He called on the armed groups in the east to lay down their arms and promised an amnesty "for those who do not have blood on their hands'.'
Talking to gangsters and killers is not our avenue.
That appeared to apply both to separatist, pro-Russia fighters in the country's east and to nationalist groups that oppose them.
Poroshenko also promised dialogue with citizens in the eastern regions, but excluded the rebels.
"Talking to gangsters and killers is not our avenue,'' he said. He also called for early regional elections in the east.
Al Jazeera's Kim Vinnel, reporting from Donetsk, said people there are divided over whether Poroshenko can create any real change in the east.
"Many people have for a long time felt alienated by Kiev," she said.
The chairman of the self-proclaimed Donetsk People's Republic, Denis Pushilin, dismissed Poroshenko's offer to call regional elections.
He told Al Jazeera that Donetsk is already in talks about becoming a part of the Russian Federation and that the fight in the east will continue until Ukrainian troops withdraw.
Government forces continued to battle rebel fighters even as the president took the oath of office.
Hours after Poroshenko was inaugurated, an aide of the Donetsk People's Republic's leader was fatally shot while in a car in front of a restaurant.
Maxim Petrukhin, the aide of Pushilin, was killed in Donetsk, with separatists claiming the act was an assassination attempt on Pushilin.
Poroshenko, the billionaire confectionary magnate, became Ukraine's fifth president since independence and its first since 1991 to win election with more than half the vote in a single round.
He says he wants closer relations with Europe, and won support and encouragement for his policies to stabilise Ukraine when he met US President Barack Obama and European leaders in Poland and France on Friday.
He also briefly met Putin in France during ceremonies marking the World War Two D-Day landings on Friday, and may have discussed a possible ceasefire with the rebels.
Putin said he welcomed Poroshenko's plans to stop the bloodshed, but said Ukraine must stop its "punitive" military operation.
Russia rejects charges by Kiev and the West that it is actively supporting the rebels in the Russian-speaking east.
The fighting since Poroshenko's election has revealed that many of the rebels are from Russia, with dozens of dead bodies of fighters sent back across the frontier.
In a small sign of a thaw, Moscow sent its ambassador - withdrawn after pro-Russian President Viktor Yanukovich was toppled in February - to Kiev to attend the swearing in.
Moscow has also begun withdrawing some of the tens of thousands of troops it had massed on the frontier.
The uprising in the east is not the only challenge facing Poroshenko, who inherits a country on the verge of bankruptcy, still dependent on Russia for natural gas, and rated by watchdogs as one of the most corrupt and ill-governed states in Europe.