PHNOM PENH, Cambodia (AP) — A prominent Cambodian environmentalist and five others were released on Monday a day after being detained while investigating illegal logging in a national park.

Ouch Leng, who was awarded a 2016 Goldman Environmental Prize, was taken into custody on Sunday along with the other activists who have documented an increase in illegal deforestation in the Veun Sai-Siem Pang National Park, located near an economic land concession in northeastern Stung Treng province.

Provincial spokesman Men Kung told The Associated Press by phone that the six were freed after signing a promise not to enter a prohibited zone again. He said they will face court if they trespass again.

Authorities have launched a broader crackdown on environmental activists in recent months. In July, 10 members of a Cambodian environmental group, Mother Nature Cambodia, who campaigned against destructive infrastructure projects and alleged corruption, were each sentenced to six years in prison on charges of conspiring against the state.

Local rights group Licadho said that the government granted an economic land concession in the area in 2022, even though it contravened a 2012 moratorium on new concessions, which have been linked to mass evictions, rapid deforestation and extraction of resources.

Cambodia’s government has long been accused of using its judiciary to persecute critics and political opponents. Prime Minister Hun Manet succeeded his father, Hun Sen, in August last year after he ruled the country for nearly four decades, but there have been few signs of political liberalization.