From Humeyra Pamuk, Jana Shaker, Ahmed Tolba, and Steve Holland

ZURICH/DUBAI/WASHINGTON, June 21 (Reuters) - Negotiators from the United States and Iran are set to begin peace talks in Switzerland on Sunday, as U.S. officials denied Iranian claims about closing the Strait of Hormuz.

Iranian state media reported that a large Iranian delegation had arrived in Switzerland for peace talks with the United States, as U.S. Vice President J.D. Vance left Washington for meetings that Pakistan said would begin on Sunday.

Although the United States and Iran agreed to a 60-day ceasefire while negotiations took place, the Iranian Revolutionary Guard announced on Saturday the closure of the Strait of Hormuz, even though the US military said commercial ships continued to pass through the waterway.

These developments could complicate talks in which the two sides are seeking to move forward with an interim agreement brokered by Pakistan and signed on Wednesday by US President Donald Trump and his Iranian counterpart Masoud Pezeshkian to end the nearly four-month-long war.

Referring to what it called Israeli "crimes" in Lebanon that violate US ceasefire commitments, the Iranian Revolutionary Guard warned that ships would be at risk if they approached the Strait of Hormuz, a vital waterway for global oil and gas supplies. However, US Central Command stated that 55 commercial vessels transited the strait on Saturday, carrying more than 17 million barrels of oil destined for global markets.

The Central Command added that US forces will ensure the continued flow of commercial shipping.

Trump wrote in a social media post on Saturday that no tolls would be imposed on passage through the strait during or after the 60-day ceasefire, unless the United States imposes tolls if peace talks fail.

Trump left the door open to the possibility of the United States imposing transit fees on the Strait of Hormuz "in return for services rendered as the guardian angel of the Middle East" if a peace agreement is not reached.

Mohammad Mokhbar, an advisor to Iran’s Supreme Leader Ayatollah Mojtaba Khamenei, accused the United States on X.com of failing to implement the first clause of its 14-point interim agreement with Iran, which includes a ceasefire “on all fronts,” including Lebanon.

He said that as long as the agreement remains just ink on paper, the flow of energy in the Middle East will remain halted.

The truce in Lebanon appeared fragile amid an exchange of attacks between the Israeli army and the Iranian-backed Hezbollah armed group.

Momentum is increasing

Iranian media reported that the Iranian delegation is led by chief negotiator Mohammad Bagher Ghalibaf and includes Foreign Minister Abbas Araqchi, as well as senior officials from the security, central bank, and oil sectors. In addition to Vance, the American negotiating team includes envoys Steve Wittkopf and Jared Kushner, Trump's son-in-law.

Iranian Foreign Ministry spokesman Ismail Baghaei said that Iran will press Switzerland to ensure compliance with its obligations, noting that the other party has failed to honor agreements in the past.

Vance said in an interview with Fox News that he was confident the ceasefire would hold and that he had seen no evidence of the Strait of Hormuz being closed.

The US vice president departed for Switzerland shortly after 4 p.m. Eastern Time (2100 GMT) on Saturday. Vance told reporters before boarding a plane at Joint Base Andrews in Maryland that negotiators would likely hold "talks that will last several days."

He added, "I hope we can make progress on the nuclear issue, and make progress on the ceasefire in Lebanon."

A ceasefire in Lebanon was one of the conditions for the start of talks between the United States and Iran on the Iranian nuclear program and other issues. However, the Lebanese Civil Defense reported that 20 people were killed in Israeli airstrikes in Lebanon on Saturday, just hours after the ceasefire was supposed to take effect.

Israel said its strikes were in response to attacks by Hezbollah, while the Iranian-backed group declared it would not allow Israel "freedom of movement" in Lebanon.

Israel, which was not involved in the talks, says it is not a party to the agreement and will keep its forces in the Lebanese territory it currently controls.

Israeli Channel 12 reported that the Prime Minister and the Minister of Defense instructed the army to cease fire in Lebanon, but without withdrawing from the areas it had captured.

A poll conducted by the Hebrew University in Israel, the results of which were exclusively reviewed by Reuters, showed that approximately 92 percent of Israelis believe Iran benefited more from the joint Israeli-American military campaign than Israel, and only about 8 percent believe Israel emerged victorious. Nearly 90 percent of Israelis said the war's objectives were not achieved, while more than 70 percent do not believe Netanyahu's claims of significant accomplishments.

Lebanon’s official National News Agency said Israeli fighter jets and drones bombed sites in southern Lebanon and the Bekaa Valley, both Hezbollah strongholds, on Saturday.

An Israeli military official said that Hezbollah fired more than 50 projectiles at Israeli forces in southern Lebanon overnight, and that Israel launched an attack on what it described as Hezbollah targets in response.

A military statement said that Israel is committed to the ceasefire, but will continue to respond to any threat to Israel or its forces.

The Lebanese Ministry of Health says 4,057 people have been killed in Israeli attacks since March 2, including medics, women and children, but it does not specify the number of combatant deaths.

Israeli authorities say at least 32 soldiers and four civilians have been killed in fighting with Hezbollah.