JEDDAH, Saudi Arabia — Saudi prosecutors have secretly filed charges of supporting terrorism and attempting to overthrow the government against 16 Jeddah residents widely known for peacefully demanding political reforms, most of whom remain detained nearly four years after their arrest, according to three sources familiar with the case.

The men’s attorney, Bassim A. Alim, said in an interview that he first heard about the charges in early August. He has been allowed by court officials to view the lengthy indictment, which also includes charges of money laundering and financing terrorism, but has not been permitted to take a copy with him.

The judge presiding over the case is part of the Specialized Criminal Court that prosecutes terrorism and state security cases. Its proceedings are held in secret with no access for the public or press.

The accusations against the 16 have not been reported in the Saudi media.

Gen. Mansour Al Turki, a spokesman for the Ministry of Interior, said he did not have an immediate response but would seek one when asked about the charges by email on Dec 13.

Unlike the hundreds of alleged militants arrested by Saudi security forces in recent years, the Jeddah group is not associated with extremist Islamist groups such as Al Qaeda, and was not clandestinely plotting violent attacks.

“They are seeking reform and to open people’s minds,” Alim said. “They are extremely anti-Al Qaeda.”

Their case underlines the narrow limits of political dissent permitted in the Saudi kingdom. Although Saudis have enjoyed a large measure of freedom to discuss social and economic issues since King Abdullah bin Abdul Aziz began his reign five years ago, criticism of the monarchy and the royal family’s unfettered privileges are not allowed.

Nevertheless, small groups of political activists seeking constitutional curbs on the monarchy, the right to form political parties and greater equality before courts have emerged in recent years. Many activists are also critical of U.S. policy in the Middle East.

One of the most prominent groups, the Riyadh-based Saudi Civil and Political Rights Association, has asked authorities for permission to stage a sit-in on Dec. 23 to demand political reforms, including an elected prime minister — a post now held by the king. But even the protest’s organizers concede they are unlikely to get that permission.

Asked for comment, Al Turki noted that “demonstrations are illegal in the kingdom.”

The aims of the reformist groups, which include both secular and Islamist-oriented activists, strike a sympathetic chord among many Saudis. But these groups do not get much open support from fellow citizens, partly because being outspoken for political reform can often lead to arrest.

On Dec. 6, Mohammed Al Abdul Karim, an assistant professor of Shariah, or Islamic law, at Imam Muhammad bin Saud University, was detained after posting an essay on his Facebook page criticizing the way royal successions are handled.

He questioned why ordinary Saudis have no choice in selecting their leaders and speculated how the kingdom’s unity might be affected if factions within the royal family fought among themselves.

Last June, a vocal human rights activist in the Eastern province, Mekhlef Al Shammary, was arrested and charged with “annoying others.” Although a court dismissed the charge, Al Shammary remains is prison.

“Annoying authorities — I don’t know what to do with this charge,” said Mohammad Al Qahtani, a co-founder of the Saudi Civil and Political Rights Association. “It’s a flagrant case of arbitrary detention. He was thrown in prison out of frustration. The authorities could not control him.”

Also, Munir Baqer Al Jassaas, an advocate for Shiite rights, has been held since November 2009 without being charged. Authorities arrested Al Jassaas after he criticized the kingdom’s treatment of Shiites in an online discussion forum.

Several of the 16 in the Jeddah group, which includes businessmen, university students, lawyers and a former judge, were arrested Feb. 2, 2007, during a meeting at attorney Essam Basrawi’s home to discuss plans to demand reforms, including the formation of a civic rights group. Others were detained around the same time in different locations.

One member of the group, Saud Mokhtar Al Hashemi, is charged with traveling to Iraq during the U.S. occupation. But attorney Alim said Al Hashemi, a physician, went there as an official representative of the Saudi Red Crescent — a counterpart to the America Red Cross — to set up a field hospital.

Another activist in the group is long-time activist and former judge Suleiman Al Rushudi. A moderate Islamist, Al Rushudi was a co-founder of the Committee for Defense of Legitimate Rights in the 1990s, one of the first groups to openly lobby for greater civil rights in Saudi Arabia.

Alim said three of the 16 have been released from detention. They include attorney Basrawi, who is representing himself, Alim said.

He said the detainees had written their thoughts about the charges against them, but that he has not been allowed to take copies of those documents with him, nor to make notes of his conversations with his clients. This is a handicap for his ability to defend them, he added, because of the lengthy charge sheet.

When the group twice appeared before the Specialized Criminal Court, Alim was not allowed to attend those hearings. “The judge said I didn’t receive clearance,” he said.

Although “the charges are extremely serious,” Alim said, some do not make sense as they rest on supposed or inferred future intentions of the defendants.

Activist Al Qahtani said the Saudi government often uses terror charges to stifle legitimate, peaceful political dissent. “It’s one of the most convenient charges,” he said. “No one will defend you and you will become hopeless.”

Al Qahtani and his civic rights group sued the Interior Ministry on behalf of detainee Al Rushudi for detaining him more than six months without charges — a violation of Saudi law. Their case was dismissed in August.

“It’s amazing that after so much talk of reform, nothing really has changed,” Al Qahtani said.

Still, attorney Alim said that he is “optimistic” that the case of his Jeddah clients “is going to be resolved soon. … It is my sincere hope that we can find a compromise.”