A report in Germany’s Der Spiegel Friday claimed Syrian President Bashar Assad is building a secret underground nuclear plant. According to the news magazine, the site is being guarded by Hezbollah, the Lebanon-based terror group supporting Assad in the civil war raging in Syria.

Der Spiegel cited unspecified security sources in making the claim and laying out the background. Back in 2007, Israel was said to have conducted a secret airstrike against a target just east of Deir al-Zor on the banks of the Euphrates River, something it never confirmed. The Kibar facility, Israel and US officials alleged, contained a nuclear reactor and was designed for military purposes.

Eventually, due to immense pressure, Syria, which is a signatory to the Treaty on the Non-Proliferation of Nuclear Weapons, allowed International Atomic Energy Agency (IAEA) inspectors into the site. The IAEA determined, despite a lack of definitive proof, that there was enough suspicious evidence to assert “the destroyed building was very likely a nuclear reactor.”

Now, says the German news magazine, Assad is back at it. According to the IAEA, Syria possesses enough natural uranium for three to five nuclear bombs, once enriched. In 2013, the Institute for Science and International Security in Washington D.C. wrote, “This large stock of natural uranium metal poses nuclear proliferation risks. It could be obtained by organizations such as Hezbollah or al-Qaida or undeclared nuclear programs of states such as Iran.”

But Kibar is no longer the focal point of Syrian nuclear activity. Now, work seems to be underway in an underground facility in an inaccessible mountain region in the west of the war-ravaged country, two kilometers (1.2 miles) from the Lebanese border, near a town called Qusayr.

The site is particularly suspicious because of its concealed entrances; its special connection to Syria’s power grid; and a deep well linking it to a lake, something which would be unnecessary in an ordinary military facility, but crucial to a nuclear site. Most notable, however, is the intercepted radio traffic in which a high-ranking Hezbollah official refers to the area as an “atomic factory”.

According to documents obtained by Der Spiegel, the facility’s code name is Zamzam, and in addition to the Hezbollah support, involvement of North Korean nuclear experts and the Iranian Revolutionary Guard is suspected.

Israel and Syria do not have formal diplomatic ties, with peace efforts initiated in the 1990s failing. Israel has opted to stay out of the current Syrian conflict, although it has continued to provide medical treatment to injured Syrians on its doorstep. Israel has been accused of airstrikes against Syria, but refuses to acknowledge them.