According to the Syrian Observatory for Human Rights, pro-Iranian militias launched four rounds at a US outpost in eastern Syria's Al-Omar oil field on Monday night, causing damage but no injuries.

The incident came after the US launched airstrikes the night before against three targets in eastern Syria and western Iraq that it claimed were used by pro-Iran militants.

According to the Observatory, “heavy artillery has been launched by the (US-led) international coalition” on the town of Al-Mayadeen, which is controlled by Iranian forces, in response to Monday night's shelling.

Meanwhile, the Syrian state news agency SANA said that “missiles... attacked a military base of the US occupying forces in the Al-Omar oil field,” but did not say who was to blame.

The previous night's strikes, according to the Pentagon, were aimed at operating and weapons storage sites in two locations in Syria and one in Iraq, all close to the international border and utilized by militias engaging in drone attacks against US interests in Iraq.

According to the Pentagon, “several Iran-backed militia groups” used the facilities, including Kataib Hezbollah and Kataeb Sayyid al-Shuhada, two Iraqi Shiite armed factions.

In recent months, there have been many attacks against US objectives in Iraq that Washington has blamed on pro-Iran forces, ranging from rocket fire to convoy attacks and, most lately, the employment of armed drones.

Iran-aligned militias operate in Iraq, where Tehran and Washington are partners, and in war-torn Syria, where Iran is a vital supporter of the Damascus dictatorship.