Iran has launched a major drone attack on Israel as Benjamin Netanyahu said the country was prepared for a “direct attack” for the first time.

The Israel Defense Forces (IDF) said Iran had launched dozens of drones from within its own territory, signalling that the long-awaited attack on Israel’s territory had begun.

Israeli forces said warships and fighter jets were on “high alert” and the US was working to help intercept the drones before they reached Israel’s airspace.

The drones launched from Iran were seen flying low as they passed over Iraq, in an apparent attempt to avoid radar detection. A loud buzzing noise could be heard on videos posted on social media as they passed overhead.

“We are closely monitoring Iranian killer drones that are en route to Israel sent by Iran,” Daniel Hagari, an IDF spokesman, said in a televised statement. 

“This is a severe and dangerous escalation. Our defensive and offensive capabilities are at the highest level of readiness ahead of this large-scale attack from Iran.” 

He added: “We are working in close cooperation with the United States and our partners in the region in order to act against the launches and intercept them.”

The Israeli military has already begun planning for a retaliatory strike on Iran or its proxy groups in the region.

Israeli civilians have been advised to monitor government alerts and follow advice from the Home Front command.

Schools across the country and beaches near Gaza have been closed “in light of the security situation,” Mr Hagari said.

He added that the IDF’s interception attempts would scramble GPS signals across the country.

The Israeli defences will involve fighter jets and navy ships, which are both equipped with anti-aircraft missiles, and Israel’s Iron Dome missile defence system.

The US has moved the USS Eisenhower aircraft carrier and three other warships closer to Israel in the northern Red Sea in recent days.

Jordan said its air defences were also ready to intercept and shoot down any Iranian drones or aircraft that violated its airspace, two regional security sources said. Mr Netanyahu, the Israeli prime minister, said: “Our defence systems are deployed, and we are prepared for any scenario, both in defence and offence.

“The State of Israel is strong, the IDF is strong, the public is strong. We appreciate the US for standing by Israel’s side as well as the support of the UK, France and many other countries.

“I established a clear principle – whoever hurts us, we will hurt them. We will defend ourselves from any threat and we will do so calmly and with determination.”

A statement from Iran’s Islamic Revolutionary Guard Corps (IRGC) reported on state television said: “In response to the recent crime of the Zionist regime against the Iranian consulate in Syria, the IRGC air forces have successfully fired tens of drones and missiles towards the occupied territories.”

However, by launching the drones from Iran, well over 1,000km away from Israel, the regime seems to have deliberately avoided the element of surprise.

Joe Biden, the US president, cut short a weekend trip to Delaware and returned to Washington to receive a briefing from his security team. Channel 12, an Israeli news network, reported that the US had been the first to warn Israel the attack was incoming.

A White House spokeswoman said the attack was “likely to unfold over a number of hours”, adding: “The United States will stand with the people of Israel and support their defence against these threats from Iran.”

Jake Sullivan, Mr Biden’s national security adviser, earlier on Saturday reiterated the US’s “ironclad” support for the defence of Israel, after the government said it had redirected some military assets there in response to Iran’s threats. 

The attack was first considered “imminent” by US intelligence on Wednesday, after Ali Khamenei, Iran’s supreme leader  said Israel “must be punished” for a strike on an Iranian embassy compound in Damascus on April 1.

The drone strike is thought to be directed at government and military buildings in Israel, not civilian targets. It is the first time that Iranian forces have directly attacked Israel, although Iran has backed the proxy groups Hamas and Hezbollah in Gaza and Lebanon.

Israel has indicated that it will strike Iran directly in response to any attack on its territory. Earlier on Saturday, Israel warned it would suffer the “consequences for choosing to escalate the situation any further”.

It was unclear whether the drone salvoes would be followed by further launches of cruise or ballistic missiles. It is thought Iran may have launched the drones well in advance of the missiles, in an attempt to ensure the weapons reach Israel at around the same time.

Iran’s most notorious drone is the Shahed, which has been deployed by Russia against Ukraine and by Houthi rebels in Yemen.