Lake Sarez was formed as recently as 1911
A study has renewed fears that a mountain lake in Tajikistan may spill over, causing potentially disastrous floods across large parts of Central Asia.
The warning comes from a research expedition by Tajik civil defence experts and Russian mountaineers which has just returned from Lake Sarez, more than 3,000 metres (9,843 feet) up in the Pamir mountains.
They say an earthquake in nearby Afghanistan could rupture the natural barrier holding back the lake, unleashing a torrent of water up to 100m (328ft) high, Tajik TV reports.
The resulting flood could surge down the Panj and Amu Darya rivers and devastate large swathes of inhabited land not only in Afghanistan and Tajikistan themselves, but also in neighbouring Uzbekistan and Turkmenistan.
The floods could reach as far down as the Aral Sea, more than 1,000 kilometres (621 miles) away.
Lake Sarez was itself created by a powerful earthquake in 1911.
Its waters are held back by the Usoi natural barrier, a wall of rocks and boulders over 500m (1640ft) high.
Scientists say the lake could disappear just as quickly as it appeared.
The expedition, organized by the Tajik Emergencies Ministry and Russia's International Mountaineering Federation, set out to investigate the likelihood of the Usoi barrier bursting.
It found that an earthquake with an epicentre in Afghanistan could send mudslides and avalanches crashing into the lake.
The resulting wave would be up to 250m (820ft) high and would force water through the lake's natural barrier, Tajik TV said.
If the barrier ruptured, the torrent would cause further landslides in the valley below.
Tajikistan has long been warning of the potential for disaster posed by the lake.
Four years ago, a team of experts funded by the World Bank and the United Nations said the lake could result in the largest flood ever seen.
Tajik President Emomali Rahmonov echoed the fears in a speech to the United Nations in 2000, saying that floods caused by the lake's rupture could make five million people homeless.
Concern has also been expressed in Uzbekistan over the potential threat to the plains of Central Asia.
The region's jumpiness is not surprising, as the area is prone to earthquakes.
In 1999, a quake centred in Afghanistan caused alarm when tremors were registered in the area of Lake Sarez.
In the mid-1990s, the lake's water level was reported to have risen to a critical point after an earthquake caused two rocky overhangs to fall into the lake.
The Russian-Tajik expedition team will publish its final report on 29 August, and a documentary made using its video material is to be shown at events around the world, Tajik TV said.
BBC Monitoring, based in Caversham in southern England, selects and translates information from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages.