A missile attack in Syria's northern region has killed 26 pro-government fighters, mostly Iranians, a Syria war monitoring group said on Monday.

The Britain-based Syrian Observatory for Human Rights said the late Sunday night attack appears to have been carried out by Israel and targeted an arms depot for surface-to-surface missiles at a base in northern Syria known as Brigade 47. The Observatory said four Syrians were also among casualties.

It said the death toll could rise as the attack also wounded 60 fighters and there were several others are still missing.

There was no immediate comment from Israel.

The attack comes amid rising tensions between Iran and Israel following an airstrike earlier this month on Syria's T4 air base in central province of Homs that killed seven Iranian military personnel. Tehran threatened to retaliate for the T4 attack.

Syria, Iran and Russia blamed Israel for that T4 attack. Israel did not confirm or deny it.

Israel Defense Minister Avigdor Lieberman said in an interview published last Thursday that his country will strike Tehran if attacked by archenemy Iran, escalating an already tense war of words between the two adversaries.

Tehran has sent thousands of Iran-backed fighters to back President Bashar Assad's forces in the country's seven-year civil war.

Iranian state television, citing Syrian media, reported the attack. The semi-official ISNA news agency, citing “local sources and activists,” said the strike killed 18 Iranians, including a commander, in a suburb of the central city of Hama.

The missiles targeted buildings and centres which likely include a weapons depot, ISNA reported.

Iran's semi-official Tasnim news agency on Monday quoted chief of Fatimayoun Brigade, an Iran-backed Afghan militia in Syria fighting alongside Iranian forces, as saying their base near Aleppo was not targeted during the strikes and they had no casualties. It did not elaborate.

Earlier on Monday, Syrian TV reported a “new aggression,” with missiles targeting military outposts in northern Syria. The state-run television reported that the missiles targeted several military positions before midnight Sunday outposts in the Hama and Aleppo countryside.

Lebanon's Al-Akhbar daily, that is considered close to the militant Hezbollah group and the Syrian government said the attack targeted “important arms depots used by the (Syrian) army and Iran's Revolutionary Guards.”

It said that missiles used in the attack appear to have been bunker buster.

Syria-based opposition media activist Mohamad Rasheed said that base that came under attack is about 10 kilometres outside the city of Hama adding that airstrike led to several explosions in the arms depot. He added that the area is known as the Maarin Mountain or Mountain 47.

Rasheed said that some of the exploding missiles in the arms depot struck parts of Hama adding that residents in areas near the base fled their homes. He said the base has been run by Iranian and Iran-backed fighters from Lebanon, Iraq, Afghanistan and Pakistan.