A German university says acclaimed Chinese artist and activist Ai Weiwei, recently released from jail in Beijing, has accepted an offer to join its faculty.

But administrators of the Berlin University of the Arts said Wednesday it is not clear when or if Ai will be permitted to leave China to take up his new post.

The globally prominent artist and government critic was arrested three months ago in Beijing and later charged with tax evasion. He was released from detention last month but has been ordered to remain in Beijing until the case is settled.

In Beijing Wednesday, lawyers for Ai's design firm told the Associated Press they will use a closed court hearing Thursday to challenge a $1.87 million tax bill handed their client shortly after his release from jail June 22. The alleged debt includes $770,000 in arrears and $1.1 million in fines, but lawyers say authorities have not provided any evidence to support the government claims.

The Berlin university says it first offered Ai a position as guest lecturer shortly after his April 3 arrest, and says it began planning for the offer late last year.