The existence of a Syrian electronic surveillance base at Al-Hara, just a few miles from the Israeli border on the Golan, has been known about for decades. And the close ties between the Syrian regime and Russia's military and intelligence agencies were never much of a secret.
But Free Syrian Army (FSA) rebels, who captured the base after a series of pitched battles over the weekend, were surprised by the level of the Russian presence at the base.
In a video released by the FSA on YouTube, photographs, maps, standing-orders and other items could be seen pinned to walls, captioned in both Arabic and Russian. They included pictures of Syrian and Russian officers working together on intelligence-gathering, as well as the symbol of Russia's military electronic intelligence directorate. There were also the names of Russian colonels who had commanded the base and photos of officials visiting from Moscow.
Most of the sensitive material seems to have been removed from the base before it fell to the rebels. From the maps and directives on the walls, it is clear that the surveillance facilities were being used to eavesdrop on communications of both Syrian rebel groups and Israeli military units.
It is believed that the information gathered was shared with the Assad regime's closest allies, Iran and Hizbollah.
Russia has long been allied with Syria, and sees the country as a strategic base in the Middle East and the Mediterranean.
Russia has a naval presence at Tartus port, in the heart of the Assad clan's Allawite stronghold, and has adamantly opposed any attempts by the West to vote on resolutions against Syria at the UN Security Council. Despite the bloodshed in Syria, the Russians have continued to supply Syria with advanced weapons.
Since the Russia-Georgia war in 2008, when President Putin warned Israeli leaders to pull out military advisers who were working with the Georgian army in a private capacity, Israel has been careful not to openly support Russia's military rivals.
This has also included a reluctance to sell arms to Ukraine, and Israel refused to even express a position on the Russia-Ukraine conflict. The two countries have extensive secret relations and Israel is also mindful of Russia's large Jewish community. Israeli leaders regularly meet Mr Putin, who has also visited Israel twice. Little is said in public about the content of these meetings.
The ever-escalating civil war in Syria, however, is another matter, as it is on Israel's border. So far, the two countries have refrained from referring to each other's alleged actions in Syria. Even when cruise missiles supplied by Russia were destroyed in what was widely believed to have been an Israeli attack, the Kremlin remained silent.
Despite the evidence of direct Russian involvement in spying on its border, the joint silence is not expected to change in the near future.
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