An airstrike Sunday night targeted pro-Iran factions in Syria, while the party responsible is unknown, the strike fits a pattern of recent Israeli strikes on Iranian targets in Syria.

The London-based Syrian Observatory for Human Rights reported on Monday that at least 18 people were killed in an airstrike that hit a border area between Iraq and Syria. The rights group suggested that those killed in the airstrikes were pro-Iran Shiite militants and that the military force responsible for the airstrike is still unknown.

The airstrike occurred in eastern Syria but no further details were reported, said the group in a statement released Monday.

Late on Sunday night, the Al Arabiya TV’s English-language website reported that the Shiite Lebanese militant party of Hezbollah claimed responsibility for gunning down an Israeli unmanned drone that hovered outside Ramyah, a town in southern Lebanon,

Monday’s unknown airstrike comes as tension in the region has mounted following last months Israeli air raids in Syria and Iraq. Israel claimed the raids thwarted imminent attacks by Shiite militias, backed by Iran’s revolutionary guard, known as the Al Quds Force.

One of the Israeli raids killed two Hezbollah operatives and prompted a limited Hezbollah retaliatory attack on northern Israel earlier this month. Hezbollah claimed that it fired a rocket on an army vehicle inside an Israeli army post. Israel responded with tens of tank shells on southern Lebanon, with no causalities reported on both sides.

On Monday, the Israeli online English-language newspaper Haaretz reported that the Israeli army identified a number of failed rocket fires launched from Syria on Sunday towards Israeli territories. The army believed that the launches were carried out by the Al Quds Force, which belongs to Iran and that the Shiite elements operated from the outskirts of Damascus.

The online newspaper noted that a statement by the Israeli army held the Syrian regime of President Bashar Al Assad responsible for any such attacks from Syrian territories.

American-owned Fox News reported last week that a new Iranian military base, called the Imam Ali compound, was being constructed at the Iraq-Syrian border. Fox News said it independently verified the claim by working with a civilian satellite company to obtain images of the base construction. The base is located near a key Iraq-Syria border crossing.

Over the past several weeks, Israel is believed to have carried out multiple airstrikes in Syrian and Iraqi territories targetting alleged pro-Iran military facilities, but Israel has not claimed direct responsibility for them.

Israeli Prime Minister Benjamin Netanyahu has, however, hinted at Israel’s responsibility for the attacks, referring to Israel’s readiness to foil any actions that are intended at the state of Israel and that Israel could expand the scope of its actions in the region.