A conservation group yesterday threatened to lodge a complaint with the Administrative Court if the government fails to put the brakes on petroleum exploration and drilling in the Gulf of Thailand by Thursday.

Oil operations were threatening not just the ecological system but also tourism in popular destinations like Koh Samui and the Pha-ngan islands, the network said.

Thousands of people yesterday lined along a road around Samui to show their opposition to the government's awarding a concession for petroleum exploration and drilling to a private company.

"The government must review the issue," Praphan Diewwanich said, as he joined the show of protest, "What if an oil leak happens?"

He is from the village of Moo 1, tambon Koh Pha-ngan, Surat Thani.

Praphan said the main income for locals came from tourism. If the flow of tourists faltered, local people would suffer badly.

The Network for the Gulf of Thailand Conservation arranged yesterday's activity.

The network's chairman, Ramnet Jaikwang, who is also the mayor of Muang Koh Samui Municipality, yesterday said he would give Prime Minister Abhisit Vejjajiva until Thursday to put the exploration and drilling on hold.

"We want to see proper environmental impact assessments (EIA) and public hearings conducted first," Ramnet said.

On July 20, he submitted a letter to Abhisit informing the premier about the network's concern and demands.

Although the concessionaire, NuCoastal (Thailand), had already conducted public hearings and its EIA successfully won a green light, the network felt there might have been irregularities.

Surat Thani Chamber of Commerce chairman Thirakij Wangmutitakul said his agency had joined the network's efforts against petroleum drilling near Samui Island because it believed the operations could harm the local environment.

Chaweng Conservation Group chairman Thanongsak Somwong said locals in the fishery and tourism sector would suffer if petroleum exploration and drilling in the Gulf of Thailand expanded.

"If one company can go ahead with this kind of operation, many more companies will conduct petroleum exploration and drilling around here too," he said.

An American tourist, Zak Magh, 42, joined the protest yesterday because he wanted to see Samui remain a tropical paradise.

"The petroleum operation could spoil the mood for tourism," he said.

As opponents to its operations staged their protest on Samui Island, NuCoastal organised a press tour of its facilities in the sea off Songkhla to show its readiness to conduct business without causing harm to the environment.

The company's EIA won approval from the authorities two and a half years ago.

NuCoastal started producing petroleum from areas covered by its concession in February last year.