Britain's interior minister ordered officials Friday to grant Chinese dissident artist Ai Weiwei a six-month visa, reversing a decision to restrict him to a short trip that had prompted condemnation from rights groups.

Home Secretary Theresa May "was not consulted over the decision to grant Mr Ai a one-month visa", a spokeswoman for her department said.

"She has reviewed the case and has now instructed Home Office officials to issue a full six-month visa. We have written to Mr Ai apologising for the inconvenience caused."

Campaigners noted that the previous visa would have allowed Ai to attend an exhibition of his work at London's Royal Academy from September but meant he would not be in Britain for Chinese President Xi Jinping's state visit in October.

Ai is China's best known contemporary artist abroad but authorities denied him a passport for four years in an apparent attempt to limit his international influence.

After he finally received his passport last week, Germany granted him a four-year multiple entry visa but Ai said on Thursday that Britain had denied his request for a six-month visa and restricted him to a three-week trip because he did not declare a "criminal conviction".

Ai said he had "never been charged or convicted of a crime".

Jigme Ugen, head of a US-based Tibetan rights group, described the initial decision to grant Ai a shorter visa as "purely a kowtow to Xi Jinping's London visit".

Ai is currently in Germany, where he has a six-year-old son.