By Natalia Antelava BBC News, Central Asia

President Nazarbayev has ruled Kazakhstan for nearly 17 years

Kazakhstan is the US's closest ally in central Asia - but Russia and China are also important partners.

All are investing heavily into the country's vast oil and gas reserves.

President Nazarbayev told the BBC he was committed to turning his country into the most prosperous and democratic in the former Soviet Union.

In his first interview to the western media in more than four years, President Nursultan Nazarbayev spoke at length about his country's cooperation with the United States.

He emphasised Kazakhstan's role in what the US calls the war on terror, and its help with the post-war reconstruction of Iraq and Afghanistan.

He also spoke about the importance of his decision to declare his country a no-nuclear zone and praised the US's help with dismantling Kazakhstan's Soviet-era nuclear arsenal.

Blind eye

Economic relations, he said, were likely to top the agenda of the Washington visit.

The US is the largest investor in Kazakhstan's oil and gas industry and with the economy growing faster than any other in the former Soviet Union, Mr Nazarbayev says he hopes to expand it further.

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But this, he said, will not come at the expense of his country's relations with its neighbours, China and Russia.

Both Beijing and Moscow are operating pipelines in Kazakhstan.

The rivalry over natural resources has turned Kazakhstan's economy into a rare post-Soviet success story.

But Mr Nazarbayev's opponents say the competition also means Washington is too willing to turn a blind eye to the lack of democratic reform.

In Kazakhstan, the media is controlled by the state and no election has been seen as free or fair.

President Nazarbayev agreed that there may be a lack of democracy in Kazakhstan, but he also described political freedom as his goal and said that the young country needed more time to achieve it.

Mr Nazarbayev rejected speculation that his own family members, some of whom are already prominent political and business figures, were preparing to succeed him.

He added that he could not ban his children from entering business or politics in the same way George Bush Senior could not prevent his son from becoming the president of the US.

But the creation of a monarchy in Kazakhstan, Mr Nazarbayev said, was absolutely out of the question.