Washington DC - A fragile ceasefire between Israel and Iran took effect early on Tuesday, with the two countries confirming an earlier announcement by US President Donald Trump.

"It has been fully agreed by and between Israel and Iran that there will be a Complete and Total CEASEFIRE," Trump posted on his Truth Social platform late on Monday, specifying that it would be introduced in stages over the following hours.

Iranian media subsequently reported that a ceasefire with Israel came into force at 7:30 AM local time on Tuesday, followed by a confirmation from the office of Israeli Prime Minister Benjamin Netanyahu.

But despite the ceasefire, the Israeli military said Iran had again fired rockets at Israel. Sirens wailed in numerous towns in the north of the country, the military said. People were urged to seek shelter, and an Israeli TV reporter said that explosions were heard.

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Israeli Defence Minister Israel Katz announced swift retaliation.

"I have instructed the Israel Defense Forces to respond forcefully to Iran's violation of the ceasefire with powerful strikes against regime targets in the heart of Tehran," Katz said in a statement.

Iran, however, denied it had launched any fresh attacks.

At least nine people were killed in the northern Iranian city of Rasht ahead of the ceasefire, according to the Tasnim news agency. A further 33 people were injured in the attack on a residential area, it wrote.

State media reported that a senior Iranian nuclear scientist was killed in Israeli attacks in the morning.

Iran's health ministry said over 600 people had lost their lives since Israel launched its unprovoked attack.

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Meanwhile, at least five people were killed and 20 others injured in an Iranian assault on Israel Tuesday morning, according to a local rescue service in Beersheba.

"On the assumption that everything works as it should, which it will, I would like to congratulate both Countries, Israel and Iran, on having the Stamina, Courage, and Intelligence to end, what should be called, 'THE 12 DAY WAR'," Trump wrote on Truth Social.

His comments came after Iran launched a largely symbolic strike on a US air base in Qatar, in retaliation to the unprecedented US bombing of nuclear sites over the weekend.