The disruptions have been going on for about three weeks, but were widely reported earlier this week. Israel’s national broadcaster Kan reported on Thursday that the disruptions have now spread to other countries, including Cyprus, Turkey and part of the Greek islands.

The pilots reportedly have alternative instruments for navigation and landing and do not need to rely on the Global Positioning System.

Unnamed Israeli security officials have told local media that the GPS disruptions, a form of electronic warfare, originate in Syria, where Russian troops and aircraft are fighting on behalf of the country’s military and President Bashar Assad.

But the Russian ambassador to Israel told Army Radio Thursday that the reports are “fake news,” and  could not be taken seriously.

The Israel Aviation Authority told Haaretz that the disruptions affect only planes in the air and not ground navigation systems. An aviation source also told the newspaper that the disruptions “do not put pilots and passengers at risk.”