LEIDSCHENDAM, Netherlands — Former Liberian President Charles Taylor on Thursday became the first head of state since World War II convicted by an international war crimes court, a legal landmark observers say sent a clear message to tyrants around the world that their days of impunity are numbered.

Taylor, 64, was found guilty on 11 counts of war crimes and crimes against humanity for sending guns and bullets to Sierra Leone rebels in return for so-called blood diamonds mined by slave labourers and smuggled across the border.

The verdicts were hailed by prosecutors, victims and rights activists as a watershed moment in efforts to end impunity for leaders responsible for atrocities.

Judges at the Special Court for Sierra Leone said Taylor's aid played a crucial role in allowing the rebels to continue a bloody rampage during that West African nation's 11-year civil war that ended in 2002 with more than 50,000 dead. The rebels gained international notoriety for hacking off the limbs of their enemies and carving their groups' initials into opponents and even children they kidnapped and turned into killers.

The verdict "permanently locks in and solidifies the idea that heads of state are now accountable for what they do to their own people," said David Crane, the former prosecutor who indicted Taylor in 2003 and is now a professor of international law. "This is a bell that has been rung and clearly rings throughout the world. If you are a head of state and you are killing your own people you could be next."

United Nations Secretary General Ban Ki-moon also hailed the judgment as "a significant milestone for international criminal justice" that "sends a strong signal to all leaders that they are and will be held accountable for their actions," said U.N. deputy spokesman Eduardo del Buey.

U.S. State Department spokeswoman Victoria Nuland agreed.

"The Taylor prosecution at the Special Court delivers a strong message to all perpetrators of atrocities, including those in the highest positions of power, that they will be held accountable," she said.

Taylor attempted to avoid trial by claiming head of state immunity in 2003, but the court rejected his claim and went ahead with his trial after his 2006 arrest.

Despite Thursday's optimism, international efforts to prosecute leaders have been spotty so far at best: Slobodan Milosevic died in his cell before he could be found guilty of fomenting the Balkan wars, Moammar Gadhafi was killed by rebels last year before he could be turned over for trial, and Sudanese President Omar al-Bashir is openly defying attempts to arrest him on international genocide charges.

In one success story, prosecutors at the U.N.'s Yugoslav war crimes tribunal are close to wrapping up their case against former Bosnian Serb leader Radovan Karadzic -- although it took more than a decade to have him arrested.

Even Crane -- a vocal supporter of efforts to hold leaders accountable -- concedes that while war crimes tribunals are independent, they are hard to separate from geopolitical realities.

Syrian President Bashar Assad's regime is widely accused of atrocities as it battles to put down a popular revolt, and yet the prospect of him or any of his generals being indicted any time soon appears remote. Syria does not recognize the International Criminal Court, meaning prosecutors there cannot intervene unless the U.N. Security Council asks them to. Russia and China would likely veto any such move.

The ICC has indicted al-Bashir for genocide in Darfur, Sudan, but he openly defies an international arrest warrant by flying to friendly nations and has recently cranked up war rhetoric in his country's border dispute with South Sudan.

Most likely the next former leader to face justice will be former Ivory Coast President Laurent Gbagbo, who is jailed in The Hague on charges of attacking political opponents as he attempted to cling to power following elections last year.

Prosecuting Taylor has proved how hard it is to bring leaders to justice. He fled into exile in Nigeria after being indicted in 2003 and was only arrested three years later. And while the Sierra Leone court is based in that country's capital, Freetown, Taylor's trial was staged in the Netherlands out of fears it could destabilize the region.

Even the prosecution was tough. There was no clear paper trail linking Taylor to rebels, and judges wound up convicting him of aiding and abetting the Revolutionary United Front and Armed Forces Revolutionary Council but cleared him of direct command responsibility over the rebels.

The global implications meant little to survivors of the war in Sierra Leone who celebrated Taylor's conviction.

"I am happy that the truth has come out ... that Charles Taylor is fully and solely responsible for the crimes committed against the people of Sierra Leone," said Jusu Jarka, who lost both his arms during the fighting in 1999 and now runs an organization for fellow amputees.

In Freetown, the capital, crowds that had gathered to watch the verdict live on television sighed with relief when the conviction was announced. Simmering anger, though, was aired through posters, including one that read: "Shame on you Charles Taylor. Give us your diamonds before going to prison."

After the judgment was read out, Taylor's attorney, Courtenay Griffiths, slammed the conviction as based on "tainted and corrupt evidence." He claimed prosecutors paid for some of the evidence.

Taylor, as usual impeccably dressed in suit and tie, said nothing in court and showed no emotion as he was convicted.

There was emotion enough at his trial as 91 prosecution witnesses outlined the horrors of Sierra Leone's war, many of them describing murders, mutilations, tortures and acts of cannibalism by rebels and the children they turned into merciless killers.

Taylor spent seven months of the trial defending his actions, portraying himself as a liberator of the Liberian people, a regional statesman and peacemaker.

Edward Songo Conteh, of Sierra Leone's Amputee and War Wounded Association, was in court to watch the verdicts. His only regret was that Taylor was not immediately sentenced. That will happen next month after a separate hearing.

The court has no death penalty and no maximum sentence. Judges have given the eight other rebels they convicted sentences as high as 52 years.

"I want to see this man behind bars for the rest of his life," said Conteh, who had one of his hands hacked off by child soldiers. AP