Comedian Volodymyr Zelensky stepped into his new role as Ukrainian president with his inauguration on Monday, launching a new era for the country wracked by war and economic difficulties.

A month after scoring a landslide election victory against incumbent Petro Poroshenko, the 41-year-old became Ukraine's youngest post-Soviet president.

In a ceremony in parliament, he placed his hand on a copy of the constitution and the Bible and pledged to "protect the sovereignty and independence of Ukraine."

He used his inaugural speech to announce that he is dissolving parliament, after wrangling with lawmakers in the lower house, in order to call early parliamentary elections, which had originally been scheduled for October.

"People must come to power who will serve the public," Zelensky said.

Critics had questioned whether Zelensky would be able to govern without a parliamentary majority. Even setting a date for his inauguration took weeks of negotiations with hostile lawmakers, whom Zelensky exasperatedly called "petty crooks".

He also vowed that his first task was to bring a ceasefire in the conflict with Moscow-backed separatists in eastern Ukraine that has so far caused some 13,000 deaths.

"We didn't start this war but it is up to us to end it," he said.

The separatist authorities have indicated that they could be ready to negotiate with Zelensky.

Dressed in a dark suit and tie, the president took a non-traditional route to his inauguration -- walking on foot from his home nearby, after saying he wanted a less pompous ceremony.

In a sign of his more informal style, he exchanged high fives with supporters waiting outside and took selfies with them.

So far little is known about his precise policies after a campaign that capitalised on public disillusionment with the political establishment and promised to "break the system".

Uniquely for a first-time president, Zelensky had played the inauguration scene before -- for laughs. He starred as a history teacher who was unexpectedly elected president in a television comedy series, "Servant of the People".

Just a few months ago, the idea that Zelensky would be inaugurated for real seemed equally unlikely.

When the actor and comedian announced his candidacy on December 31, few took it seriously, but after an unprecedented campaign largely waged through social media, he won more than 73 percent in the second round on April 21, trouncing Poroshenko.

Poroshenko led Ukraine for five years, overseeing the fallout over Russia's annexation of Crimea and the armed conflict in the country's east.

While Poroshenko averted complete collapse and launched a series of key reforms he was widely criticised for failing to improve Ukrainians' living standards or effectively fight all-pervasive corruption.

Zelensky has vowed to continue the country's pro-Western course but beyond that his programme is still sketchy and his team largely unknown. His critics question how he will deal with the enormous challenges of the separatist conflict and ongoing economic problems.

The leader of one of the self-proclaimed separatist republics in Ukraine's industrial Donbass region, Denis Pushilin, on Friday told Russia's RIA Novosti news agency that he was "ready for dialogue" with the new authorities in Kiev, "naturally taking into account the interests of Donbass".

Nevertheless he condemned what he called "destructive" statements by Zelensky's team and accused Kiev of "blocking the peace process" which has long stalled.

Ukraine's allies have given Zelensky a warm welcome, but one Ukrainian site specialising in international affairs, Evropeyska Pravda, suggested this was a "hug strategy" to ensure he continued to pursue a rapprochement with the West.

The new president will immediately have to deal with a number of sensitive international issues, giving him a foretaste of the challenges lying ahead.

Three days after Zelensky's election, the Kremlin announced it was easing procedures for those living in the eastern separatist regions to gain Russian citizenship. Many observers in Kiev saw this as Moscow issuing a challenge to Zelensky and he strongly condemned the move.

In a sign of possible tensions between Kiev and Washington, Ukraine's key ally against Moscow, US President Donald Trump's personal lawyer Rudy Giuliani this month cancelled a visit to Kiev, saying Zelensky is "surrounded by people who are enemies of the (US) president." The febrile political situation prompted one pro-Western lawmaker, Serguiy Vysotsky, to warn Zelensky that the inauguration "isn't the end of your adventures -- it's just the beginning".