Expressing "deep regret" for his actions, an Islamic extremist pleaded guilty Monday to orchestrating the destruction of historic mausoleums in the Malian desert city of Timbuktu.

Ahmad Al Faqi Al Mahdi, wearing a dark suit and striped tie, stood and calmly told judges he was entering the guilty plea "with deep regret and great pain" and advised Muslims around the world not to commit similar acts, saying "they are not going to lead to any good for humanity."

The guilty plea was a landmark for the court, which has struggled to bring suspects to justice since its establishment in 2002. It was the first guilty plea and the first time prosecutors have launched a trial for the crime of deliberately attacking buildings of religious or cultural significance.

"Our cultural heritage is not a luxury good," Prosecutor Fatou Bensouda told the three-judge panel. She said Al Mahdi's guilty plea "will set a clear precedent, sending an important and positive message to the entire world."

She compared the case to the destruction last year of historic ruins in the Syrian city of Palmyra by Islamic State extremists.

The court can't bring charges in that case because Syria is not a member of the court and the U.N. Security Council hasn't called for an ICC investigation, court spokesman Fadi El Abdallah said.

Al Mahdi led a group of radicals that destroyed 14 of Timbuktu's 16 mausoleums in 2012 because they considered them totems of idolatry. The one-room structures that house the tombs of the city's great thinkers were on the World Heritage list.

Al Mahdi faces a maximum sentence of 30 years imprisonment, but prosecutors say they will seek a sentence of nine to 11 years. Judges will issue a verdict and pass sentence at a later hearing.

Prosecutors showed judges photos and videos of rebels wielding pick axes, sticks and axes to attack a mosque's door and small, brick-built mausoleums in the city. Among them were images of Al Mahdi, at times with a Kalashnikov rifle slung over his shoulder, directing the attacks, which reduced the historic structures to piles of rubble.

Prosecutors say Al Mahdi was a member of Ansar Dine, an Islamic extremist group with links to al-Qaida that held power in northern Mali in 2012. The militants were driven out after nearly a year by French forces, which arrested Al Mahdi in 2014 in neighboring Niger.

Human rights activists have welcomed the case, but criticized prosecutors for failing to file more charges against Al Mahdi.

The International Federation for Human Rights (FIDH) said its member organizations have documented a litany of crimes and filed a criminal complaint on behalf of 33 victims in Malian courts accusing Al Mahdi and 14 others of crimes including rape and sexual slavery.

"We ... deeply regret that the charges against Al Mahdi were not widened to include crimes against the civilian population, including sexual and gender-based crimes, whose victims are far too often ignored during accountability processes," FIDH member organizations said in a statement ahead of the trial.

Speaking after Monday's hearing, Bensouda said further charges could follow in her Mali probe.

"We are also investigating other crimes," she said. "So this is the first case we've brought and we will see with respect to other crimes that have been committed within the context in Mali."

On the eve of the hearing, Timbuktu's mayor, Halle Ousmane, welcomed the prosecution.

"Justice has been done," Ousmane said. "We thank almighty God and all our partners, all those who have helped with his arrest so that today justice can be done."