Airplanes, apparently unmanned, had attacked positions of Shiite militias in the Syrian city of Al-Bukhmal near the Iraq-Syria border on Wednesday afternoon, an Iraqi security official told Sky News late Wednesday.
The source said five people were killed in the attack and another nine were wounded.
The official added that militia forces have begun to take precautionary measures in light of the ongoing strikes, preventing large gatherings and deploying heavy weapons at security sites in the event of further attacks.
Al-Bukhmal border crossing is located near a key bridge on the Euphrates River. It is an important - perhaps the most important - section of the land corridor Iran is operating through Iraq to the Syria and Lebanese coasts.
Logistical supplies and missiles from Iran are believed to be delivered to Hezbollah through this route, as well as to the additional front against Israel that the Revolutionary Guard has established in Syria.
A source from Deir al-Zor military council said that the attack was carried out by an UAV, which he believes belongs to the international coalition or to Israel, and that the attack targeted bases belonging to the Iranian Revolutionary Guard, Lebanon's Hezbollah organization and other Iraqi factions.
Beirut-based newspaper Al Akhbar said the sites belonged to Hezbollah.
The report comes a day after another attack at one of the sites in the area. A few hours later, the Syrian Observatory for Human Rights, a Syrian opposition organization based in the United Kingdom, reported that at least 10 people were killed in the attack.
At noon, the pan-Arab Al Mayadeen network reported another assault in the area, with no casualties.
According to the Observatory, the base was used by Iranian and Iraqi militias backed by the Iranian regime and was attacked from the air by planes of unknown origin.
The target was reportedly a missile depot. The Al-Hadath TV channel quoted an Iraqi government source as saying that there were loud explosions at the site during the night.
Observatory director Rami Abdul Rahman said that, "Israel is behind the attack on Iraqi militias and Revolutionary Guard in the al-Bukhmal area."
Iraqi Prime Minister Adil Abdul Mahdi said Wednesday that the investigation into recent attacks on Iraqi territory is ongoing. He said Iraq had not turned to the UN Security Council over the issue as there is no hard evidence that one particular agent is operating on its territory.
"We need solid evidence and cannot rely solely on media reports," he said. As such, he added, Iraq is working to improve its air defense systems.