ADDIS ABABA (Reuters) - At least 40 people were killed by paramilitary forces in eastern Ethiopia over the weekend, a senior regional official said on Monday, in the latest spate of violence driven by ethnic divisions.

Unrest first broke out along the border of the country’s Somali and Oromiya provinces in September, displacing nearly a million people, though the violence had subsided by April.

On Monday, the Oromiya regional administration’s spokesman Negeri Lencho said heavily armed members of a paramilitary force from the Somali region had carried out cross-border attacks in Oromiya’s East Hararghe district.

“We still do not know why Liyu forces raided the areas on Saturday and Sunday,” he said, referring to the paramilitary soldiers. “But we know that all the victims were ethnic Oromos. At least 40 were killed in the attacks.”

A week earlier, mobs looted properties owned by ethnic minorities in the Somali region’s capital Jijiga. The central government said the unrest had been stoked by regional officials who had fallen out with central authorities trying to address rights abuses in the region.

The spokesman said the officials had said the government was illegally forcing them to resign, and that Liyu forces had taken part in the attacks under their orders.

The forces are seen as loyal to the region’s leader Abdi Mohammed Omer, who has since resigned.

Authorities in the Somali region were not immediately available for comment.

Ethnic violence has spread in the diverse country of 100 million people, where anti-government protests broke out in the Oromiya region over land rights in 2015. Hundreds were killed by security forces over a two-year period.

The violence is the biggest domestic challenge facing reformist prime minister Abiy Ahmed, who took office in April.

In a separate incident, a stampede among thousands who attended a visit by a prominent political activist in the town of Shashemene killed three people on Sunday, officials from the Oromiya regional government said.

The event was held to mark the return to Ethiopia of Jawar Mohammed, an activist who had been in exile in the United States but played a key role in mobilizing Oromo youths through social media.

Amid the chaos, another person was beaten to death by a mob after rumors circulated he had carried a bomb, residents said. “Police did not take action while all that took place,” the witness told Reuters. “It is an example of the lawlessness that is taking root in the country.”