JERUSALEM, Feb 15 (Reuters) - Israel has closed four of its diplomatic missions temporarily, in what one security source said on Tuesday could be linked to the anniversary of the assassinations of two Lebanese guerrilla masterminds.

A Foreign Ministry official said the missions had been closed as a temporary measure, a step seen as unusual given the routinely high security at Israeli embassies and consulates.

The official would not specify which missions had been closed, but said security alerts had been issued in eight countries: Egypt, Turkey, Azerbaijan, Georgia, Ivory Coast, Mali, Mauritania and Venezuela.

Unusual occurrences have been identified recently around a few Israeli missions abroad. Our assessment, at this point, is that these sites are under threat, and this is being taken care of, a ministry statement said.

The relevant Israeli authorities are in touch with the relevant authorities in the countries concerned, it added.

A security source linked the move to a Feb. 11 advisory issued by Prime Minister Benjamin Netanyahu's office which cited an enhanced threat of terrorist attacks against Israeli and Jewish targets abroad.

The advisory said Lebanon's Hezbollah was observing the anniversary of the 1992 death of its leader, Abbas Mussawi, in an Israeli helicopter ambush, and a 2008 car-bombing in Damascus that killed the group's guerrilla commander, Imad Moughniyeh.

Hezbollah blamed Israeli agents for the latter attack -- amid denials from Israel -- and vowed revenge at the time.