Chinese artist and dissident Ai Weiwei has a metaphor for the travel ban that will prevent him attending the growing number of exhibitions of his work being held around the world as his renown increases.

"I can swim, but not far," Ai told AFP of the ban on leaving China imposed last week despite the expiry of a year-long bail term. "I hope I can travel. This is an important part of freedom. This is also a human right."

A year after he was freed from unofficial detention, the outspoken 55-year-old artist, who has become a thorn in the side of the Chinese government, clearly chafes at the continuing restrictions on his freedom.

In an interview with AFP at his studio in Beijing Ai, who spent 81 days in custody last year, described his frustration at the ongoing case against him.

"I have a lot of art activities, design and construction in the next one or two years which will be overseas because they are not permitted domestically. Limiting me from leaving China will influence these events."

Ai was detained last year as police rounded up activists amid online calls for Arab Spring-style protests in China.

On his release on June 22, 2011, authorities accused him of tax evasion and barred him from leaving Beijing for a year -- a restriction that has prevented him from attending a number of his own exhibitions.

Ai has just missed an opening at London's Serpentine Gallery for a pavilion with a floating platform roof and an interior clad in cork which he co-designed by communicating on Skype.

He had hoped to attend an October show at the Hirshhorn Museum in Washington and take up an invitation to teach in Berlin.

But last Thursday police told him that unresolved cases involving accusations of spreading pornography, practising bigamy and conducting illegal foreign exchange transactions supported the overseas travel ban.

"These three things are just an excuse not to give me the right to go outside China," he said.

The pornography charges stem from what he called a joke after he challenged two groups of visitors to take nude photos with him, which were posted online.

He is married, but had a relationship with another woman -- cited by authorities as bigamy -- with whom he had a child, and officials have threatened they could detain him again.

"They are used to doing things this way," said Ai, who is technically allowed to travel within China outside his home city of Beijing, but whose passport is being held by authorities.

He described the move as revenge against him, but said it would also hurt China which is seeking to build soft power through spreading culture abroad.

"China's policy has always emphasised soft power. This will stop China's cultural exchanges and projects," he said.

Ai has previously riled the ruling Communist Party with high-profile investigations into the collapse of schools in the 2008 Sichuan earthquake and into a 2010 fire at a Shanghai high-rise that killed dozens of people.

Shanghai later demolished Ai's newly built studio in the commercial hub and he was beaten by police in Sichuan after he tried to testify on behalf of another activist who investigated the school issue.

Ai said his desire to travel overseas did not necessarily mean he would choose a life in exile, like many other Chinese dissidents.

"This is not to say I must leave China," he said.

Asked about the case of blind activist Chen Guangcheng, who left for the United States to study in May after taking refuge in the US embassy, Ai replied: "I don't like the US embassy because the structure is too ugly," referring to the fortress-like compound in Beijing.

He is now challenging the tax evasion charges and a multi-million-dollar penalty brought against Beijing Fake Cultural Development Ltd., a company he set up but which is registered in his wife's name.

A court hearing last week lasted more than nine hours and a ruling is expected by early August.

Ai compared the court fight to how Chinese authorities reportedly used to charge the families of executed criminals for the bullets.

"It doesn't matter how wrong they are, they put all the cost on you -- cost of money, cost of energy, passion and your will. It's wasted because you cannot deal with this big machine."

He hopes for change, but he questions how much his activism has been able to accomplish. "According to logic, there should be change because this society has already reached a time when it must change," he said.

But he added: "It's like (being) against the wall. I have raised consciousness, that's all."