KHARTOUM, June 12 (Reuters) - Sudanese authorities on Sunday closed down Sudan's only English-language opposition daily, the Khartoum Monitor, and withdrew its licence, the chairman of the paper's board said.

Alfred Taban, whose paper focuses mostly on southern issues, said a supreme court judge had told him by letter that the paper's licence had been withdrawn, overruling an appeal court decision two years ago to allow it to continue to publish.

"We did not even know that it had gone to the supreme court -- this information was not communicated to us," Taban told Reuters. The board will appeal against the ruling, he added.

The Khartoum Monitor has been briefly closed down many times over the past two years. Recently it was suspended for one day for printing an article about violent clashes in a camp south of Khartoum between police and refugees, most of them from the south and the troubled Darfur region.

Taban said the attorney-general had some years ago brought a case against the paper which, as a result, had its licence withdrawn. The board appealed against the verdict and in 2003 the court of appeal overturned the lower court ruling and restored the paper's licence.

But the paper, one of only three independent dailies in Sudan, has since suffered repeated censorship and closure, Taban said.

The attorney-general was not immediately available for comment.

"We are going to appeal for the reversal of this decision," Taban said. "This court is acting two years late."

He said the ruling contravened the principle of freedom of the press enshrined in the peace deal signed in January between the former rebel Sudan People's Liberation Army (SPLA) and the government to end more than two decades of civil war in southern Sudan.

The deal does not cover a separate conflict in Sudan's wertern Darfur region.

The Comprehensive Peace Agreement (CPA) allows for a new coalition government to be formed, expected on Aug. 9, as well as wealth and power sharing and a referendum after six years in which the south can opt to secede.

Taban said the closure might have been ordered because the paper often published calls from southerners to split from the north, or because his board had been talking to the international community about censorship of the press, which the government denies exists.