Banda Aceh – The trials of two foreign women accused of associating with separatist rebels in Indonesia's troubled Aceh province began on Monday with prosecutors saying they had violated visa regulations.

Briton Lesley McCulloch and American Joy Lee Sadler have been in police custody for more than two months and face a maximum five years in jail or a fine of 25 million rupiah for the immigration offences.

"Lesley has violated the visa permit and has been charged with activities of collecting data or documents related to GAM," chief prosecutor Kamar Zaman told the court in the provincial capital Banda Aceh, referring to the Free Aceh Movement (GAM) rebels.

Both women have denied wrongdoing and said they were maltreated during their detention – accusations authorities have rejected.

McCulloch, accompanied by her lawyer and a representative of the British embassy, appeared relaxed and smiled to journalists during the court session, which lasted for about 30 minutes. The beginning of Sadler's trial immediately followed.

A lawyer for the women said his clients wanted the case to end as soon as possible so they could go home.

Asked if they would plead not guilty, lawyer Johnson Pandjaitan said: "Yes. Our clients have said that they visited Aceh as tourists." Indonesian troops picked up the pair on September 11 in a security sweep in the remote southern part of Aceh, where GAM rebels have been fighting for independence for decades.

The trials are due to continue in Banda Aceh, 1,700 km northwest of Jakarta on Wednesday when witness statements will be heard.

McCulloch lectures at the University of Tasmania in Australia and has written academic papers on Aceh. Sadler is from Waterloo, Iowa, and has nursing experience with refugees in conflict zones.

The trials begin as tension remained high in the staunchly Muslim province on the northern tip of Sumatra island, where police shot dead four rebels in a village in western Aceh on Sunday.

Aceh police spokesman Taufik Sugiyono said the clash happened during a patrol by security forces. "The police and military were patrolling in the area. Four GAM members were killed and there were no casualties from our side," Sugiyono told Reuters.

International mediators say the two sides are expected to sign a fresh peace deal on December 9, which observers hope will end years of violence in which thousands of people have been killed.

More than two years of peace talks brokered by the Geneva-based Henry Dunant Centre have failed to end the violence with several ceasefire agreements ignored by both sides.