The United States and Iran engaged in renewed military conflict on June 26, local time, just nine days after formally signing a memorandum of understanding (MOU) to end their hostilities.

With both sides exchanging fire while continuing follow-up negotiations following the MOU, the ceasefire agreement appears to be facing a critical challenge.

In a statement posted on X (formerly Twitter) on the same day, U.S. Central Command (CENTCOM), which oversees U.S. forces in the Middle East, stated, "U.S. Central Command forces conducted airstrikes against Iran on June 26 as a firm response to the attack on a merchant vessel passing through the Strait of Hormuz on June 25."

CENTCOM explained that U.S. aircraft struck Iranian missile and drone storage facilities, as well as coastal radar sites.

The June 25 attack by Iran, which the U.S. cited as the justification for its strike, refers to a drone attack on the Singapore-flagged container ship "Ever Lovely" as it attempted to pass through the Strait of Hormuz.

CENTCOM criticized the action, stating, "The Iranian military's unjustified attack on a merchant vessel is a clear violation of the ceasefire." It added, "Furthermore, Iran's dangerous behavior has undermined freedom of navigation at a time when commercial traffic through this vital international trade route is increasing."

"CENTCOM forces continue to provide safe passage coordination and support for merchant vessels transiting the Strait of Hormuz," the command added. "U.S. forces remain stationed and vigilant in the region to ensure that the agreement with Iran is observed, implemented, and fully effective in all aspects."

U.S. Vice President JD Vance wrote on X, "Iran signed a ceasefire agreement. We have been adhering to that agreement." He added, "If they (Iran) have disagreements on how the MOU is implemented, they can call us. But we will meet violence with violence."

Prior to this, U.S. President Donald Trump also criticized Iran's attack on the merchant ship in the Strait of Hormuz as a "clearly foolish violation of the ceasefire agreement," signaling the possibility of a response.

Iran did not remain idle following the U.S. airstrikes.

The Islamic Revolutionary Guard Corps (IRGC) labeled the U.S. attack on that day a "violation of the ceasefire" and announced that it had struck U.S. military bases in the Middle East.

In a statement released on June 27, local time, the IRGC announced, "Following the Zionist regime's (Israel) violation of the ceasefire in southern Lebanon, the U.S. regime, which breaks its promises, has also violated the (ceasefire) agreement, as it always does." It added, "In response to this aggression, the IRGC Navy has struck several U.S. terrorist military bases in the region."

The IRGC further confirmed the U.S. attack against them, stating, "The U.S. attacked the Iranian coast under various pretexts, citing the passage of a violating vessel that was using an unauthorized route in the Strait of Hormuz."

Earlier, Iranian state television reported on June 26 that a communication tower in the southern Iranian port city of Sirik, adjacent to the Strait of Hormuz, was hit by two projectiles.

State television also reported that two projectiles landed on Qeshm Island in the Strait of Hormuz.

The source of the projectiles was not mentioned.

Ebrahim Azizi, Chairman of the National Security and Foreign Policy Committee of the Iranian Parliament, also claimed on X on June 27, "The U.S. has attacked Iran again during negotiations," adding, "The failed U.S. President has not upheld the principles of negotiation or the ceasefire."

Azizi further argued that according to Article 5 of the Islamabad Agreement (the peace MOU), control procedures and authority over passage through the Strait of Hormuz belong to Iran. He warned that the U.S. is attempting to violate this in various ways and that if such violations continue, Iran will respond more broadly.

The peace MOU, which was agreed upon by the U.S. and Iran on June 14 and took effect after formal signing on June 17, mandates an immediate and permanent end to military operations on all fronts.

Since then, both sides have been conducting follow-up negotiations regarding Iran's nuclear program and the lifting of sanctions against Iran.

However, as Israel continued its attacks on the pro-Iranian militant group Hezbollah in Lebanon, the negotiations faced crises, including temporary postponements. With this latest exchange, the peace MOU appears to be put to the test before the ink has even dried.

The U.S. attack on Iran is primarily read as a warning message to Tehran.

The Trump administration's top goal in pursuing peace with Iran through the MOU was the normalization of passage through the Strait of Hormuz. It appears that when Iran's attack on a merchant ship disrupted transit again, the U.S. sent a strong message of deterrence through military action.

Iran's counter-strike on U.S. bases after being hit by U.S. forces is interpreted as a signal that they did not agree to the MOU from a position of weakness, and that they will not easily concede in future negotiations with the U.S. regarding denuclearization and the lifting of sanctions.

With the U.S. midterm elections approaching in November, the Trump administration faces significant political pressure regarding the resumption of war, and Iran also views the MOU as a favorable achievement. Therefore, both sides may be cautious about escalating the conflict to the point of scrapping the peace agreement.

However, concerns are growing that if both sides, lacking mutual trust and conscious of domestic public opinion, continue a "tit-for-tat" military response, they could face unpredictable situations—such as significant military casualties—that could lead to the collapse of the precarious MOU framework between the two countries.