The United States struck southern Iran on Thursday, drawing retaliation from Tehran against a U.S. military base, in the most serious clashes since an April ceasefire began.

Iran condemned on Thursday what it called violations by the United States after its strikes on the southern port city of Bandar Abbas, while vowing to defend its sovereignty.

Hezbollah said its fighters clashed with Israeli forces in a town north of the Litani river on Wednesday, a day after Israel's military said it was expanding its ground operations in the country's south.

Israeli strikes on southern Lebanon killed 31 people on Tuesday, the Lebanese health ministry said, as Israel said it was intensifying attacks despite a truce in its war with Hezbollah.

Iran's Revolutionary Guards on Wednesday said a return to war with the United States was unlikely, while warning that the Islamic republic stood ready against any attack.

Israel said on Wednesday it had killed the new head of Hamas' armed wing in Gaza, Mohammed Odeh, after killing his predecessor earlier this month despite an ongoing ceasefire.

Since Hamas' October 2023 attack, Israel has systematically targeted the group's leaders, both in Gaza and across the region.

Israeli forces have begun operating beyond their so-called "Yellow Line" in south Lebanon, which runs around 10 kilometers (six miles) deep inside Lebanese territory, a military official confirmed to AFP on Tuesday.

The health ministry said Tuesday that an Israeli strike a day earlier killed at least 11 people, two of them children, as the Israeli military said it had launched strikes on Hezbollah infrastructure.

In a statement, the ministry said that "yesterday's Israeli enemy airstrike on the town of Mashghara in West Bekaa resulted in a preliminary toll of 11 martyrs, including two girls and a woman, and 15 wounded, including a child", adding that rescuers were still clearing the rubble in the eastern town.

The Israeli military warned residents of the southern city of Nabatiyeh to immediately evacuate on Tuesday ahead of expected strikes, despite a ceasefire.

"For your safety, you must evacuate your homes immediately and move north of the Zahrani River. Anyone who is near Hezbollah members, facilities or military equipment is putting their life at risk!" the military's Arabic-language spokesman, Avichay Adraee, posted on X.

Iran's Islamic Revolutionary Guards said on Tuesday that they had downed a U.S. drone and shot at other aircraft entering the country's airspace.

U.S. military aircraft "entered Iranian airspace in the Persian Gulf region, and air defense units of the Islamic Revolutionary Guard Corps... identified and shot down an MQ-9 drone," the Guards said in a statement on their Sepah News website.