In late April 2018, rumors were circulated holding that an “Israeli airplane in Syria has dropped the first nuclear bomb deployed in armed conflict since the US dropped atomic bombs on Hiroshima and Nagasaki in 1945”:

Tens of pro #Assad fighters, mostly #Iranians, killed in attack on #Syria bases in Hama and Aleppo. Raids probably carried out by #Israel using Tactical Nuke – Registered as M2.6 Earthquake, but #Syrian media says US & Brits launched attacks from Jordan https://t.co/uylNAEb6BW pic.twitter.com/3mxrlhZ1sT — Adam Milstein (@AdamMilstein) April 30, 2018

One disreputable conspiracy web site (responsible for a number of “doomsday” rumors) similarly asserted:

RUSSIA CONFIRMS IT WILL RETALIATE BY FORCE — MASSIVE EXPLOSION HITS IRANIAN BASE IN SYRIA – FEARS ISRAEL USED TACTICAL NUKE — REGISTERED AS M2.6 “EARTHQUAKE” At around 3:40 PM Eastern US time on [29 April 2018], an utterly MASSIVE explosion took place at an Iranian base inside Syria. The photo above was taken from 5 kilometers (about 3 MILES) away, and well-into the explosion which “seemed to linger.” There are now widespread BUT UNCORROBORATED rumors Israel used a Tactical Nuclear Bomb against the Iranian base.

Similarly, the fake news site Your News Wire picked up on this rumor and published an article reporting that:

An Israeli airplane in Syria has dropped the first nuclear bomb deployed in armed conflict since the US dropped atomic bombs on Hiroshima and Nagasaki in 1945, according to local reports. The nuclear blast targeted an ammunitions depot in Hama, Syria and was so powerful it caused a 2.6 magnitude earthquake recorded close to Taqsees, Hama, Syria at 10:40 pm local time [on 29 April 2018], at the same time Syrian TV reported several explosions in the same area.

That article included embedded video of the purported nuclear explosion but elided its original description, which mentioned nothing about the deployment of nuclear weapons:

Multiple credible news outlets reported Iranian casualties after a missile strike in northern Syria on 29 April 2018. However, none of those sources mentioned the use of a “tactical nuke”:

A missile attack on government outposts in northern Syria killed more than a dozen pro-government fighters, many of them Iranians, a war monitoring group and an Iranian news agency said [on 30 April 2018]. The strikes came amid soaring tensions between regional archenemies Israel and Iran. There was no official confirmation of the death toll or what was the target. The [29 April 2018] night strikes sparked speculation on who carried it out, with most reports suspecting Israel was behind it. Syrian state TV called it a “new aggression on military positions” in Hama and Aleppo provinces but was not specific. Activists said there was a spectacular explosion at an arms depot and military compounds where Iranian fighters are based. The explosion was large enough to be picked up by monitors as a magnitude 2.6 earthquake.

The Syrian state news agency SANA did report a “hostile [rocket]” attack had occurred in that country, but their report also made no mention of any nuclear detonation:

Syrian state media say an overnight missile attack in the country’s northern region has killed 26 pro-government fighters, mostly Iranians. The Syrian news agency SANA on April 30 quoted a military source as saying positions in the provinces of Hama and Aleppo had been “subjected to a new aggression with hostile missiles.” The Syrian Observatory for Human Rights, based in Britain, says the attack appears to have been carried out by Israel and that it also targeted an arms depot for surface-to-surface missiles at a base in northern Syria known as Brigade 47. The Observatory says four Syrians were also among casualties.

The use of atomic bombs by the U.S. against Japan at the end of World War II in 1945 marked “the first and last time that nuclear weapons have been used in warfare.” Modern usage of “tactical nuke[s]” would be globally newsworthy, but no credible news source reported such, nor did either Syrian state media nor the Facebook page responsible for uploading footage of 29 April 2018 missile strikes against Syria make any such claim.