"Following the identification of irregular activity of Iranian forces in Syria, the IDF (Israel Defence Forces) has decided to change the civilian protection instructions in the Golan Heights and instructs local authorities to unlock and ready shelters in the area," the army said in a statement.

"Additionally, defence systems have been deployed and IDF troops are on high alert for an attack."

The announcement came shortly before US President Donald Trump made public his decision to withdraw from the Iran nuclear deal.

Israel has been accused of carrying out a series of deadly strikes on bases in Syria out of which Iranian forces operate.

It is concerned over the growing presence of Tehran's forces and those of Iran's Lebanese ally Hezbollah on Syrian territory.

In an interview late last month, Israeli Defence Minister Avigdor Lieberman vowed to strike at any attempt by Iran to establish a "military foothold" in Syria.

Israel seized 1,200 square kilometres (460 square miles) of the Golan Heights from Syria in the Six-Day War of 1967 and later annexed it in a move never recognised by the international community.

The two countries remain technically at war.