MANILA (Reuters) - Leaders of the Philippines’ mainstream separatist group on Sunday urged Muslims in the country’s south to support a new autonomy law designed to tackle extremism and defuse a half-century of conflict in a referendum later this year.

The Moro Islamic Liberation Front (MILF), which signed a peace deal with the government four years ago, gathered tens of thousands of supporters from all over the southern province of Mindanao to its base to begin a massive campaign for the law’s approval.

President Rodrigo Duterte last signed the new autonomy legislation, called Bangsamoro Organic Law, allowing self-rule for Muslims in 2022, hoping to end a conflict that has killed more than 120,000 people and displaced 2 million.

“Our real journey toward self-determination is just starting,” Mohagher Iqbal, the rebel group’s chief negotiator, told Reuters by telephone, saying there are still challenges ahead that could stop the implementation of the law.

Speaking earlier to thousands of supporters, including women and children, he asked them to vote for the approval of the law expanding the territories covered by the Muslim autonomous area in the south, although he warned of some potential obstacles.

“We still don’t know if there are groups or individuals who will question the new autonomy law before the Supreme Court,” he told a cheering crowd in a speech livestreamed on social media. Supporters chanted “Allahu Akbar” and “Yes to BOL” in the rebel camp in the middle of coconut and banana groves.

In 2008, close to a million people were displaced in central Mindanao region when violence erupted after the Supreme Court canceled a deal on ancestral domain with the MILF. A small but more radical splinter rebel group has since emerged, and has aligned with pro-Islamic State militant forces.

MILF leaders said they are trying to avoid a similar episode that could lead to extremist groups taking hold in the south. The rebel group is expected to dominate the 80-member Bangsamoro transition government that will be formed after the referendum.

The Bangsamoro area includes part of the Philippines’ second-largest island of Mindanao, and a chain of dozens of small islands to the west notorious for piracy and banditry.

An estimated five million Muslims live in the region, which has the predominantly Catholic nation’s lowest levels of employment, income, education and economic development.

The United Nations, European Union, United States and Japan welcomed the passing of the new autonomy law, hoping for an end to violence and a start to the region’s economic reconstruction.