Hackers targeted the website of an Israeli newspaper early Monday, on the anniversary of the killing of a prominent Iranian general.
The hackers replaced the content of the Jerusalem Post with an image that threatened a site associated with Israel's undeclared nuclear weapons programme.
Top Iranian general Qassem Soleimani was killed by a US drone strike in Iraq two years ago.
While no group immediately claimed responsibility, the image posted on the Jerusalem Post's website included a missile coming down from a fist bearing a ring long associated with Qassem Soleimani.
The image included an exploding target from a recent Iranian military drill designed to look like the Shimon Peres Negev Nuclear Research Center near the city of Dimona.
The facility is already home to decades-old underground laboratories that reprocess the reactor's spent rods to obtain weapons-grade plutonium for Israel's nuclear bomb program.
Under its policy of nuclear ambiguity, Israel neither confirms nor denies having atomic weapons.
In a tweet, the Jerusalem Post acknowledged being the target of hackers.
“We are aware of the apparent hacking of our website, alongside a direct threat to Israel,” the English-language newspaper wrote. “We are working to resolve the issue; thank readers for your patience and understanding.”
As the head of the Quds Force of the Revolutionary Guard, Soleimani led all of its forces and frequently shuttled between Iraq, Lebanon and Syria. US had accused him of plotting attacks on its forces.
There was no immediate response from the Israeli government. The hack comes after Israel's former military intelligence chief in late December publicly acknowledged his country was involved in Soleimani's killing.