Authorities in a devoutly Islamic district of Indonesia's Aceh province have distributed 20,000 long skirts and prohibited shops from selling tight dresses as a regulation banning Muslim women from wearing revealing clothing took effect.

The long skirts are to be given to Muslim women caught violating the dress code during a two-month campaign to enforce the regulation, said Ramli Mansur, head of West Aceh district.

Islamic police will determine whether a woman's clothing violates the dress code, he said.

During raids, Islamic police caught 18 women travelling on motorbikes who were wearing traditional headscarves but were also dressed in jeans. Each woman was given a long skirt and her pants were confiscated. They were released from police custody after giving their identities and receiving advice from Islamic preachers.

"I am not wearing sexy outfits, but they caught me like a terrorist only because of my jeans," said Imma, a 40-year-old housewife who uses only one name. She argued that wearing jeans is more comfortable when she travels by motorbike.

Motorbikes are commonly used by both men and women in Indonesia.

"The rule applies only to Muslim residents in West Aceh,"Mr Mansur told. "We don't enforce it for non-Muslims, but are asking them to respect us."

He said any shopkeepers caught violating restrictions on selling short skirts and jeans would face a revocation of their business licenses.

No merchants have been seen displaying jeans or tight clothing in stores in West Aceh district in recent weeks.

The regulation is the latest effort to promote strict moral values in the world's most populous Muslim-majority nation, where most of the roughly 200 million Muslims practice a moderate form of the faith.