Diplomats from Iran and the three European parties remaining in a moribund 2015 nuclear deal met in Istanbul on Friday, Iranian and British officials said, their first round of talks since the U.S. began nuclear talks with Tehran in April.

US President Donald Trump said on Thursday that Washington is “very close” to reaching a nuclear deal with Iran after Tehran “sort of” agreed to its terms.

Envoys for Iran and the United States have engaged in four rounds of talks. But exactly what a deal would look like remained unclear.