The Grand Mosque of Brussels. (Emmanuel Dunand/AFP/Getty Images)

A Belgian court announced Tuesday that it had struck down an effort to deport an imam at Belgium's oldest mosque, saying that Belgian immigration authorities had not provided evidence the cleric posed a serious threat to society.

The imam, Abdelhadi Sewif, has worked at the Grand Mosque of Brussels for 13 years. The Belgian state secretary for asylum and migration, Theo Francken, accused Sewif of threatening national security as he sought to reject a residence permit renewal. Sewif has denied the charges and said that he was never able to review the evidence against him, because it was classified intelligence material.

The decision curbs the efforts Belgian authorities have started to make against the mosque, which is Belgium's largest and is leased by the Belgian government to the Saudi royal family. Belgian lawmakers and counterterrorism officials have raised concerns about the unusual arrangement of foreign control of the mosque, which they say makes it less accountable to national authorities.

The Belgian parliamentary committee charged with investigating the causes of the March 22, 2016, bombings of the Brussels airport and subway recommended in October that Belgium break the lease, which was signed in the 1960s as a gesture of goodwill to the country's growing Muslim population.

But Belgian counterterrorism officials have said they have no evidence that the mosque's imams have advocated violence or lawbreaking. Tuesday's announcement from the court, which followed a formal Friday court decision, said that authorities failed to provide specific evidence that Sewif was a danger to security.

Authorities must demonstrate "how the personal conduct of the person concerned concretely constitutes present, real and sufficiently serious threat as to affect the fundamental interest of society. Such a proof cannot be based on mere speculation or general considerations," the immigration court wrote in announcing its decision. "The existence of such a threat is not demonstrated in this case."

Sewif denied the charges against him in an interview last month, saying he had always advocated an inclusive vision of Islam.

On Tuesday, Sewif's lawyer said the imam welcomed the ruling.

"We are happy about the decision," said Hicham Chibane, the lawyer. "Imam Sewif is a person of dialogue, a tolerant person."

Although the ruling halts the effort to force Sewif to leave the country, it remains unclear whether Belgian immigration authorities will seek to expel the cleric using different reasoning. Sewif's residence permit expired over the course of the court procedures.

"We are analyzing the court decision, and after that we can decide on the next steps to take," said Katrien Jansseune, a spokeswoman for Francken.