Iran's Islamic Revolutionary Guards Corps (IRGC) Khatam al-Anbiya Central Headquarters has said it has closed the Strait of Hormuz to shipping again, citing what it called US violations of the war-ending memorandum and continued Israeli attacks in southern Lebanon, Qods Online reported on June 20.

"Due to the blatant breach and violation by the United States of the first clause of the ceasefire agreement, and in response to the continuous and relentless violations of the ceasefire by the Zionist (Israel) regime in southern Lebanon, the merciless killing and displacement of hundreds of thousands of oppressed people of this land, and also considering the failure of the Zionist (Israeli) occupying forces to withdraw from southern Lebanon, it is announced that the Strait of Hormuz will be closed to vessel traffic," the IRGC announced. 

The move marks a sharp escalation that threatens to unravel the deal that ended more than three months of conflict between Tehran and Washington and reopened the strait only days earlier, removing the demonstrated leverage Iran holds over one of the world's most critical oil chokepoints. The announcement also comes as Israel continues to strike southern Lebanon in an attempt to tackle Hezbollah, but has complicated talks between Iran and the US set for today in Switzerland.

In a statement, the central headquarters said the strait would be closed again in light of clear US bad faith over the non-implementation of the first clause of the memorandum, and in response to continued ceasefire violations by Israel in southern Lebanon, the killing and displacement of civilians, and the failure of Israeli forces to withdraw from southern Lebanese territory.

This was the first step in responding to the enemy's breach of the agreement, the statement said, with further steps planned if aggression continued in order to force compliance with the deal's commitments.

The Revolutionary Guards' navy separately warned that vessels failing to observe the designated shipping route south of Larak Island would bear responsibility for any incident, from striking a mine to maritime collisions or being targeted.

The escalation followed comments by Foreign Ministry spokesman Esmaeil Baghaei, who said an Iranian delegation would travel to Switzerland to press the other side over implementation of its commitments. The trip to Geneva was not the second phase of negotiations but solely for signing the memorandum in person, Baghaei said.

Iran had abided by its commitments while the other side was obliged to halt the war in Lebanon and had failed to do so, Baghaei said, describing the first clause as the most important part of the memorandum.

If part of the other side's commitments were not implemented, the whole agreement would face problems, and the other side should take the necessary measures as quickly as possible, he said.

Iran had not signed an agreement for it to go unimplemented, Baghaei said, describing Tehran's approach as commitment for commitment and warning that Iran would respond with the necessary measures if the other side refused to act.

According to Yaron Avraham from Israel's Channel 12, Marco Rubio is expected to call Benjamin Netanyahu in the next few minutes to outline the US demands in Lebanon amid the ceasefire agreement with Iran.