Nigeria's Jonathan sworn in

ABUJA (AFP) - Nigerian President Goodluck Jonathan was sworn in on Sunday following an election seen as the fairest in nearly two decades, pledging transformation for a divided country hit by deadly post-poll riots.

Jonathan took the oath amid tight security at a colourful ceremony with a military parade and fly-over in the capital of Africa's most populous country. About 10,000 security personnel were deployed and mobile phone services cut.

Some two dozen African heads of state looked on in Abuja's Eagle Square as the fedora-wearing Jonathan declared that "transformation begins today" in the continent's largest oil producer, long held back by deeply rooted corruption.

"Together we'll unite our nation and improve the living standard of all our peoples, whether in the north or in the south, in the east or in the west," he said in his inaugural address.

"We will not allow anyone to exploit differences in creed or tongue, and set us one against another," he added later, drawing applause from the crowd of several thousand, some of whom wore dresses with pictures of Jonathan emblazoned on them.

The 53-year-old southern Christian comfortably beat his main opponent, ex-military ruler Muhammadu Buhari from the mainly Muslim north, in the April 16 vote, but three days of rioting followed which killed more than 800 people.

The rioting and massacres spread across the north, with victims hacked, burnt or shot to death. Mobs torched churches and mosques, beat people after pulling them from cars and attacked shops.

Jonathan, who originally came to power following the death of his northern predecessor Umaru Yar'Adua in May 2010, called on losing presidential candidates to "join hands with me as we begin to transform our country."

Buhari's party is challenging Jonathan's victory in the courts.

While Jonathan spoke of improving Nigeria's woeful electricity supply and unleashing the economic potential of the vast nation, suspicion remains in the north, poorer and less educated than the oil-producing south.

Many from the region accuse Jonathan's ruling People s Democratic Party of vote rigging and reject observers' reports calling the election a step forward for Nigeria despite major flaws still to be addressed.

Many northerners had put their hopes in Buhari, who alleged fraud in the election, but disassociated himself from the violence.

Security was extremely tight at the inauguration venue, with roads blocked for several kilometres. Twin car bombs went off outside the same square during last October's independence celebrations, killing at least 12 people.

A total of 10,000 police, military and state security services personnel were deployed, backed by at least two helicopters.

As an additional security measure, mobile phone services were suspended at Eagle Square following a government directive, according to a message sent to clients. They did not appear to be working in other parts of the capital as well.

Among those present were newly elected Ivorian leader Alassane Ouattara, Yoweri Museveni of Uganda, Jacob Zuma of South Africa and Robert Mugabe of Zimbabwe.

Former colonial power Britain was represented by Minister for Africa Henry Bellingham, while Assistant Secretary for African Affairs Johnnie Carson represented the United States.

It is not only the north that poses potential troubles for Jonathan, the first president from the oil-producing Niger Delta region.

The Niger Delta has seen relative peace after years of unrest thanks to a 2009 amnesty deal, but questions have been raised over how long it can last. Jonathan pledged in his inaugural address that he would make peace in the region a priority.

A deadly conflict between Christian and Muslim ethnic groups in the country's middle belt region also continues to simmer, while an Islamist sect has been blamed for dozens of killings in the northeast.