Overnight strikes targeted a factory where pro-Iranian groups are based, "causing huge explosions", the Britain-based Syrian Observatory for Human Rights (SOHR) said. "Sixteen people, among them Syrians and non-Syrians, were killed," the UK-based monitor said, without specifying whether the dead were fighters.

The NGO had initially reported a provisional toll of 12 dead.

Since the start of Syria's civil war in 2011, Israel has carried out hundreds of strikes against President Bashar al-Assad's regime and Iranian-backed groups supporting Damascus.

The Syrian defence ministry said in a statement that "after midnight... the Israeli enemy carried out an aerial attack... targeting certain positions near Aleppo".

The SOHR said the area hit in Hayyan was "controlled by pro-Iranian groups made up of Syrians and non-Syrians".

Israeli strikes have intensified since the start of a war on May 10 between Israel and the Palestinian Islamist movement Hamas in the Gaza Strip.

Israeli authorities rarely comment on such strikes on Syrian territory.

On April 1, a strike attributed to Israel targeted the Iranian consulate in Damascus, killing several Iranian officials.

Tehran retaliated on April 13 with an unprecedented missile attack on Israel.

After the Iranian response, the intensity of Israeli strikes on Syria decreased, before picking up again in May, according to the SOHR.

The Syrian Observatory for Human Rights has counted 44 strikes attributed to Israel against Syria, most of them air raids, since January.

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