Factbox-What is Iran’s ‘Axis of Resistance’, which groups are involved?

In one of the latest such attacks, three U.S. servicemen were killed and at least 34 wounded in a drone attack by Iran-backed militants in northeastern Jordan near the Syrian border, U.S. Central Command said on Sunday. An umbrella group of hardline Shi'ite Muslim armed groups close to Iran, the Islamic Resistance in Iraq claimed an attack near the Syrian-Jordanian border around the same time U.S. officials said their troops were targeted. They have claimed more than 150 attacks on bases housing U.S. forces in Syria and Iraq since October, leading to dozens of mostly minor injuries and drawing several rounds of U.S. strikes in response.