Dissident artist Ai Weiwei says continuing pressure from the Chinese government is preventing him from attending an exhibition of his work in the United States.

The first major American exhibition of Mr Ai's works is being held in Washington ahead of a four-city tour of North America.

In 2011, he spent 81 days in detention amid a roundup of Chinese activists, and last August a court upheld a $2.4 million tax evasion fine against him.

Mr Ai has told he lives under constant pressure from the Chinese government.

"They will not let me leave the nation, they still kept my passport," he said.

He claims he is being followed, his phone is being tapped and he cannot get access to the internet.

"They secretly detained me without a real excuse, so it is extremely difficult - not only my situation, but a lot of people - writers, internet users - have been taken by police, and the whole situation is not getting better."

In November, China underwent a once-in-a-decade leadership transition, installing Xi Jinping as the new general secretary of the Communist Party and incoming president of China.

But Mr Ai says he is not expecting things to be different under the new leadership.

He says he does not believe there will be major changes in Chinese society until its leaders are decided democratically.

"Whatever and however they change the leadership, it's not done by the process of democratic decisions - it's done in a very secretive way and nobody understands what is going to happen," he said.

"Without democracy China has so much problems - in recent days you see the air conditions in Beijing - environmental problems and resource problems, and education and corruption.

"The change is there gradually, but not from the state power, but rather... from a young generation that believes in freedom and they are not easily controlled, because this is the internet age."