According to US administration officials, there is also an internal power struggle underway in Tehran that has made it difficult to achieve and maintain an agreement with Iran.
A hardline, uncompromising faction within the Iranian power elite that is trying to sabotage the ceasefire is behind the Iranian attacks on three merchant ships this week, the sources say. The power struggle in Tehran is said to have begun after the US and Israel attacked Iran and killed the country's supreme leader, Ayatollah Ali Khamenei.
The sources also say that US President Donald Trump will give US negotiators limited time to reach an agreement with Iran, but they emphasize that the president has a range of options if the talks fail.
But Iran's UN Ambassador Amir Saeid Iravani told reporters outside the UN building in New York that all activities in the Strait of Hormuz are "controlled exclusively by Iran."
Iran has previously said that the Strait of Hormuz must be under Iranian control and that ships wishing to pass through the strait must pay fees to Tehran.
