For the small group of rich Russians, an exclusive voyage through the Galapagos Islands in a mini-submarine should have been the climax of their luxury yacht tour of the southern seas.

But their trip ended last week with the seizure of the British-owned mini-sub hired for the cruise, the detention of its British owner and eight other crew and, it is claimed, the arrest of the Russians' superyacht in Panama.

The trip's organisers and the mini-sub's operators, Silvercrest Submarines, have been accused of illegally entering the Galapagos, the world's most heavily protected environmental reserve, and its crew face up to a month in custody.

"The use of submarines in the Galapagos National Park is forbidden," said Edwin Naula, the park's head of tourism.

The Ecuadorian Navy impounded the mini-sub and its support vessel, the Cebaco Bay, in the harbour on the island of San Cristobal, leaving Alan Whitfield, the sub's owner, a British colleague and seven Cebaco Bay crew confined to the ship.

Lawyers are heading out to the islands, but the status of the Russians' hired superyacht is less clear. The 24 Russians are believed to have paid $120,000 for a four-hour voyage around the islands, and even paid for the mini-submersible to be specially flown out for the trip.

Whitfield's wife, Jan, said her husband was adamant that his contract stipulated the tour organisers would arrange for all the necessary diving and submarine permits needed. He was now trying to prove this to the park authorities.

She said he alleged that as soon as the Ecuadorian Navy appeared to intercept the mini-sub, the Russians' yacht, the Qatar-based Constellation, set sail. It was then seized in Panama.

The incident has highlighted a growing problem for the Galapagos: the dangers posed to its unique and highly sensitive flora and fauna from a dramatic growth in "green" tourism.

This week the UN will hear demands by ecologists for the Ecuadorian Government to enforce stricter controls on tourism, illegal fishing and economic development in the archipelago.

Visitor numbers have soared in the past 25 years, reaching more than 100,000 last year. Tour vessels and fishing boats are blamed for bringing invasive species to the islands, destabilising their delicate ecological balance. Visits are supposed to be strictly controlled, with ships even fumigated and quarantined before they arrive to prevent alien species or diseases being carried in.

The UN's World Heritage Site conference is meeting in Vilnius, the capital of Lithuania, this week to add other globally important cultural and ecological sites to the 812-strong list of designated World Heritage Sites.

But it is thought that the UN's environment advisers, the World Conservation Union, may demand that the UN put the Galapagos on the List of World Heritage in Danger - 34 places including Cologne Cathedral, the ancient Iranian city of Bam, struck by an earthquake in 2003, and an ancient religious site in Afghanistan.

"This is a delicate political situation," said one delegate to the event.

Inen Meliane, from the Conservation Union in Ecuador, added: "There needs to be stricter marine tourism management. It's such a huge reserve, the capacity to control it needs to be strengthened."