Iran said it has closed the Strait of Hormuz for shipping transit due to what it called Israel’s violation of a ceasefire, even as Pakistan said US-Iran talks were set to open in Switzerland on Sunday.

The Hormuz action casts a new cloud over the talks, which are aimed at permanently ending a conflict that’s thrown the Middle East into disarray. The immediate impact on vessel traffic was unclear, but even before the recent ceasefire, millions of barrels of oil had been quietly escaping the waterway each day.

Iran’s joint military command said the closure is Iran’s first step in response to Israel’s continued attacks in southern Lebanon, the semi-official Tasnim news agency reported on Saturday.

Negotiations on a peace deal were meant to start on Friday, but were delayed after fighting between Israel and Iran-backed Hezbollah militants in Lebanon intensified. Iranian state TV reported Saturday that a delegation was now en route to the talks, which Pakistan’s foreign ministry said will open on Sunday.