Putin gave the order on Saturday to prevent illegal border crossings, the Interfax news agency reported citing Kremlin officials.

Ukraine claims that many of the insurgents in its restive east have come from Russia - a border which has a reputation for being poorly guarded. In his inauguration speech on Saturday, Poroshenko said he was prepared to set up a corridor for the safe passage of "Russian militants" out of the country.

Ukraine's new chapter

Poroshenko took the oath of office in front of guests from more than 50 countries, vowing to "preserve and strengthen Ukraine's unity" as he faces the challenge posed by pro-Russian separatists in the east of the country.

He appealed to armed groups in the east to lay down their arms and offered amnesty "for those who do not have blood on their hands," while also stressing the importance of rebuilding Ukraine's relationship with Russia.

"The citizens of Ukraine will never feel the blessing of peace and security until we resolve our relations with Russia," Poroshenko said.

But he also said that there would be no compromise with Moscow on the status of the Crimean peninsula, which Russia annexed in March after a controversial referendum appeared to show a majority of residents in favor of leaving Ukraine.

"Crimea has been and will remain Ukrainian," he said, adding that he had "put that clearly to the Russian leader in Normandy," referring to a meeting with President Vladimir Putin on the sidelines of D-Day commemorations in France on Friday.

Boosting EU ties

Poroshenko also said he intended very soon to sign the economic part of an Association Agreement with the European Union, saying he saw this as a first step to full membership.

His predecessor in office, Viktor Yanukovych, was ousted in February after sometimes violent street protests after he rejected an EU Association Agreement in favor of closer ties with Moscow.

Poroshenko was elected on May 25 as the country's fifth president since independence in 1991 with more than 54 percent of the vote.

Rebel leaders in Ukraine's east dismissed Poroshenko's speech.

"He is the president of another country," the self-declared prime minister of the insurgent Donetsk People's Republic, Alexander Borodai, told the RIA Novosti news agency. "This statement doesn't concern us.

dr,tj/jlw (AP, dpa, AFP, Reuters)