Viktor Yushchenko was sworn in as president of Ukraine in a historic ceremony capping months of turmoil in the former Soviet republic that he now intends to set on a firm pro-Western course.

The 50-year-old former central banker read aloud the oath of office inside parliament with his right hand placed on the Constitution and the Bible.

The chamber erupted into chants of "Yu-shchen-ko! Yu-shchen-ko!," the battle cry of the mass "orange revolution" protests that carried him to power, as soon as he finished.

"The newly-elected President of Ukraine Viktor Andreevich Yushchenko has taken the oath to be true to the Ukrainian people and has assumed the post of president," Mykola Selivon, head of the constitutional court, said after the chants had quieted down.

"The Ukrainian citizens have achieved honest elections," he said in a short speech afterward. "The transfer of power is legitimate. It is a great national victory."

Yushchenko becomes the third president of an independent Ukraine, taking over after a decade of authoritarian-leaning rule by Leonid Kuchma, who was present in the chamber.

He has promised to turn Ukraine, under Russian influence for centuries, towards western Europe and attending the ceremony was an array of foreign dignitaries supporting his efforts, including outgoing US Secretary of State Colin Powell, NATO chief Jaap de Hoop Scheffer and presidents of several former Soviet republics or satellite states, including Estonia, Lithuania, Poland and Romania.

After a short speech in parliament, Yushchenko received the commanders of the armed forces and then headed to Kiev's central Independence Square, the epicenter of the "orange" protests that roiled the nation and captured the attention of the world.

His supporters from throughout Ukraine had poured into the plaza, decorated in cheerful orange flags of his campaign and the nation's blue and yellow standard, since morning.

"I couldn't be here for the revolution, I was on the election commission back home," said Nina Marushak, a 50-year-old accountant who arrived in Kiev from Odessa with two friends.

"We accomplished what we set out to do -- we got a president whom we chose. I helped make history in my country and I wanted to see it in person."

Yushchenko's inauguration ends months of political turmoil that split this nation and sparked Cold War-like exchanges between neighboring Russia and the West during a vicious election campaign that saw him nearly die from a poisoning attempt.

Washington, which along with Europe backed Yushchenko in his standoff with the authorities following a disputed runoff vote in November, vowed to help him in his reform drive.

"The United States will help him," Powell told reporters as he flew to Kiev late Saturday. "We would like to give as much assistance as we can."

Sunday's ceremonies mark a personal triumph for Yushchenko, who at the beginning of the election campaign in September nearly died from what doctors later said was deliberate poisoning with dioxin that grotesquely disfigured his face.

After a November runoff, Yushchenko refused to concede defeat to Viktor Yanukovich, a prime minister who was annointed successor by Kuchma and openly supported by Russian President Vladimir Putin, saying the vote had been rigged.

Hundreds of thousands of people clad in the orange color of his campaign poured into Kiev's freezing streets in organized peaceful protests to support him.

The supreme court eventually threw out the poll because of fraud and ordered a new ballot for December 26, which Yushchenko easily won.

Soothing frazzled nerves in a furious and humiliated Russia, Ukraine's largest trading partner and key energy provider, will be among the most urging tasks facing Yushchenko's administration.

He will begin his presidency with a visit to Moscow on Monday for talks with his Russian counterpart, before setting off on a four-day European coming-out tour.

PHOTO CAPTION

Ukraine's President-elect Viktor Yushchenko holds the Bulava, Ukraine's historical symbol of power, that was handed to him by Cossacks during a ceremony in downtown Kiev on the eve of his inauguration. (AFP)