Switzerland has given Turkey notice to honour pledges made over the construction of a controversial dam in the southeast of the country.
The state-run Export Risk Agency said it had sent a letter with an Environmental Failure Notice, which could ultimately lead to the withdrawal of an international consortium - including four Swiss firms - from the Ilisu project.
It is the first time that Switzerland, alongside Germany and Austria, has taken this action.
Turkey has 60 days to fulfil more than 150 international standards benefiting from insurance cover, but the deadline can be extended. The measures halts further construction on the project.
Switzerland granted an export risk guarantee worth SFr225 million ($199 million) in March.
Independent experts and development aid groups have repeatedly warned that Turkey has failed to respect international standards over social, environmental and cultural issues.
The Ilisu dam is part of a larger hydro-power project in the mainly Kurdish region and will result in the resettling of up to 60,000 people.