KHARTOUM (Reuters) - Dozens of journalists and Sudan's national press body protested against the dismissal of the editor of one of the country's biggest independent newspapers by the security service, staging a rare challenge to the dominant security apparatus.

On Thursday, Al-Nour Ahmed al-Nour, editor of al-Sahafa newspaper, said security agents came to his office to order him to leave his job after accusing him of insulting one of their colleagues.

Nour has stopped working since then, and the newspaper, one of Sudan's oldest, has removed his name from the masthead.

On Monday, more than 70 journalists staged a sit-in in front of the newspaper's head office in central Khartoum to demand the security service reinstate Nour as editor, witnesses told Reuters.

The reporters, which were from different newspapers, held placards reading: "No to security censorship of newspapers" and "No to suspension of journalists", they said.

In a separate action, the National Press Council, a quasi-official body which is in charge of licensing newspapers and has little power, called on the presidency to reverse Nour's dismissal.

"The council considers it (the dismissal) as one of the forms of direct interference of the security services in its duties ... apart from the suspension of some papers and the censorship of others," the council said in a statement late on Sunday.

Sudanese journalists complain of frequent restrictions, even though censorship was officially abolished in the Arab-African country in 2009.

The security service, which was not available for comment, often bans distribution of entire editions to inflict financial losses on newspapers as punishment for critical coverage, journalists say.

Sudan's constitution guarantees press freedom but editors say the security service expect them to clear main stories before publication every day.

(Reporting by Khalid Abdelaziz; Writing by Ulf Laessing in Cairo; Editing by Mohammad Zargham)