The inauguration was broadcast live on national TV

Leaders from 70 countries, including eight presidents, attended the lavish and colourful ceremony.

In a brief speech, Mr Nazarbayev repeated his goal to make Kazakhstan "one of the world's 50 most competitive states".

The international community has said December's election was not democratic.

Nr Nazarbayev pledged to "serve Kazakhstan's people, respect laws and the constitution of Kazakhstan, and guarantee the rights and liberties of its citizens".

Speaking in the presidential palace in the capital, Astana, he then bent to kiss the national flag, before a long round of applause from the audience.

Mr Nazarbayev has headed the oil-rich Central Asian state since 1989 - two years before independence.

He is deemed to have brought Kazakhstan prosperity and stability but to have concentrated power in the hands of close associates and trampled the opposition.

The BBC's Central Asia correspondent, Ian MacWilliam, says much of the focus at Mr Nazarbayev's inauguration was on oil.

Reports suggest the Ukrainian leader Victor Yushenko wants to discuss possible routes for new gas pipelines from central Asia to Ukraine to lessen his country's dependence on Russian gas.

The Karachaganak gas field in Kazakhstan is one of the world's largest and is due to significantly increase production in the next few years.

Central Asia's leaders would also like new export routes for their abundant gas and oil. Currently, they can only export their gas through Soviet-era pipelines through Russian territory.

With more control over their export pipelines, the Central Asians could demand world market prices.