The battles of Mosul in Iraq and Aleppo in Syria could see an expansion of the area controlled by allies of Iran. Israeli military officials are concerned that the advance of Shia militias, led by Iranian Revolutionary Guard officers - involved in both battles - could be part of the realisation of a long-held plan to create a "Shia Crescent" stretching from Iran's borders to Hizbollah's strongholds in Lebanon.

While the battle being waged by an international coalition against Daesh around Mosul and the bloody siege of Aleppo are far from over, the involvement of Iranian-controlled militias in both campaigns is causing concern within Israel's security establishment.

"As far as Iran is concerned, these are its new defence lines," says a senior Israeli officer. "It will cling to them with everything it has, even though the campaign is causing them and Hizbollah to lose a lot of the support they used to have in the Arab world."

An overland corridor from the Persian Gulf to the Mediterranean not only bolsters Iran's influence in the region, but will serve as a route to send arms to its proxies, chief among them Hizbollah.

Iran has maintained two major arms smuggling routes over the past two decades.

One was by air, to Damascus airport, and from there by road to Hizbollah's arsenals in Syria and the Bekaa Valley in Lebanon. This route still exists but, as the war in Syria has raged, Hizbollah has been less confident about storing its strategic weapons in the country. Meanwhile, there has been a series of air-strikes on Hizbollah arms convoys from Syria to Lebanon, which has been attributed to Israel. Another problem with this route is Iran's limited air-cargo capacity.

Until two years ago, larger quantities of munitions were shipped from Iran's ports in the Persian Gulf to Sudan via the Arabian Peninsula. From there they were smuggled overland and then by ship from Egyptian or Libyan harbours to Lebanon.

A combination of Saudi pressure on the Sudanese government and air strikes - again attributed to Israel - has prompted the Sudanese to close their borders to Iranian shipments.

The new overland route through northern Iraq and Syria has the advantage of being relatively far from Israel's northern frontiers.

A major point of concern for Israeli military planners is that in addition to the recent deployment of a Russian S-300V air-defence battery in Syria - on top of an S-400 battery Russia deployed there last year - the Shia Crescent route is deep within the area covered by Russian air power, and under the protection of the Assad regime and other allies of the Kremlin.

Over the past year, Israel has coordinated its operations over Syria with the Russians, but as the United States has a new policy which could include an effort to enforce a no-fly zone over northern Syria, the situation may be about to change. Carrying out strikes against arms convoys in the Shia Crescent corridor could become much more difficult.