A man looks at the wreckage of an Iranian missile that landed in Israel on Monday. AP
According to AFP, a large blast struck near Iran's Foreign Ministry headquarters in central Tehran, followed by a series of explosions believed to be linked to air defence activity across parts of the capital.
"The exact location and source of this explosion are still unknown," local media outlets, including Fars News Agency, reported, adding that air defence systems had been activated in several areas of Tehran.
Iranian media later reported that a "hostile drone" had been shot down over the capital.
"A hostile drone belonging to the American-Zionist enemy was targeted and destroyed by air defences in the skies over Tehran," Mehr News Agency reported, without providing further details.
Meanwhile, Iran's Islamic Revolutionary Guard Corps (IRGC) said it had targeted Israel's Nevatim and Tel Nof air bases, as well as a petrochemical facility, in retaliation for an Israeli strike on a similar site in southwestern Iran.
The IRGC warned that Israel had "initiated a dangerous game, the scope of which will encompass all energy-related targets in the region."
In Israel, air raid sirens sounded across large areas of the north and centre, while explosions were heard over Jerusalem early Monday, AFP journalists reported.
The Israeli military said it had carried out strikes on several targets within a petrochemical complex in Mahshahr, southwestern Iran.
"The strikes and the damage to the complex disrupt its ability to manufacture various types of weapons," the military said in a statement.
It added that Israeli forces had also targeted Iranian air defence systems.
An Israeli military official said Iran had launched nearly 30 ballistic missiles towards Israel since Sunday night, marking the first exchange of fire between the two countries since a truce was reached in April.
"Last night, the Iranian regime began firing ballistic missiles towards Israel... They fired close to 30 ballistic missiles towards Israel," the official told journalists, adding that Yemen's Houthi group had separately launched two missiles at the country.
The latest escalation comes at a critical moment, with diplomatic efforts led by mediator Pakistan hanging in the balance.
Iranian Foreign Ministry spokesman Esmaeil Baqaei told a press conference in Tehran attended by AFP that it was "perfectly natural that the diplomatic process initiated to put an end to this imposed war would be affected."
Tehran had earlier vowed retaliation after Israel carried out strikes on Beirut's southern suburbs on Sunday, despite reported US efforts in recent days to prevent further escalation.
Monday marked the 100th day of the conflict, which began on 28 February when Israel and the United States killed Supreme Leader Ayatollah Ali Khamenei and several senior Iranian officials.
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