Israel says it has launched a preventative attack against Iran, its defence minister has said. 

Israel Katz declared a state of emergency and described the attack as being done "to remove threats", the Reuters news agency reports.

It comes as witnesses in Tehran say they heard an explosion, according to the Associated Press.

Iranian state television acknowledged the explosion without providing more details. 

Sirens also sounded across Israel, which the country's military said was a "proactive alert to prepare the public for the possibility of missiles being launched toward the state of Israel".

The Israel Defence Forces said that sirens sounded all throughout the country in the last few minutes, "with an advance instruction alert directly to cellular devices to stay within proximity to protected spaces". 

"This is a proactive alert to prepare the public for the possibility of missiles being launched toward the State of Israel," they add.

"The IDF emphasizes that the public is requested to stay in proximity to protected spaces."

After defence minister Israel Katz announced the country's preemptive strike on Iran, the Israel Defence Forces announced ​a "prohibition ‌on educational ​activities, gatherings, and workplaces". 

"Essential ​sectors" were ​exempted, ​the military ⁠said.