Saudi military forces have committed grave abuses against civilians in an eastern province of Yemen over the past year, including torture, forced disappearances and arbitrary detention, Human Rights Watch said in a report released Wednesday.

The New York-based watchdog presented chilling testimony from former detainees in Yemen’s remote eastern province of al-Mahrah, which borders Oman and Saudi Arabia. Several Yemenis told HRW they were held and tortured at a secret detention center in the provincial capital. The report documented 16 cases of arbitrary detention and at least five cases of detainees who had been “forcibly disappeared” for months, transferred illegally to neighboring Saudi Arabia.

“Saudi forces and their Yemeni allies’ serious abuses against local al-Mahra residents is another horror to add to the list of the Saudi-led coalition’s unlawful conduct in Yemen,” said Michael Page, deputy Middle East director for HRW. It’s the latest report of civilian abuse in the regional proxy war in Yemen that has killed more than 100,000 people over five years and pushed the Arab world’s poorest country to the brink of famine.

Yemen’s internationally recognized government, which is backed by Saudi Arabia, was driven from power in 2014 as the Shiite Houthi rebels captured the capital, Sanaa, and much of the country’s north. A U.S.-backed Arab military coalition launched an air offensive against the Iran-backed Houthis to restore the government. Rights groups have accused both parties of systematic rights violations, as well as war crimes.

HRW did not receive a response from the Saudi-led coalition about the alleged abuses.

Al-Mahrah, although located far from the heavy fighting in the country, has recently become a flashpoint between local residents and Saudi troops. Saudi and Saudi-backed forces have arrested scores of Yemenis who have thronged the streets in the province to protest the growing Saudi military presence in the area. The demonstrations frequently devolve into violence as troops disperse people with live bullets.

Former detainees told HRW that Saudi-backed Yemeni troops had snatched them from the streets and taken them to informal detention centers. There, they were beaten and tortured with electric shocks until they confessed to fabricated charges and pledged to cease all opposition activities.

Many described harsh conditions in detention. One journalist, identified in the report only as Bassem, said that Saudi officers tortured him with electric shocks and deprived him of food in a filthy cell that was “like a garbage dump.”

Mothers of men who were abducted and transferred to Saudi Arabia said that months had passed without word of their sons. Then they suddenly received calls from prison phones in Saudi Arabia, where numerous Yemenis continue to be held without charge.

Page, the deputy regional director, urged the Saudi and Yemeni governments to release civilians wrongfully detained and investigate the accusations of widespread abuse, as required by international law.