BEIRUT (Reuters) - As Iran vows to take revenge for the killing of one of its top military commanders, Major General Qassem Soleimani, it can count on the support of groups that are part of a Tehran-led alliance across the region.
In Lebanon, Yemen and the Gaza Strip, Iran-backed groups have fought U.S. allies including Saudi Arabia and Israel, while in Iraq the United States has recently accused Iran-backed fighters of targeting U.S. personnel directly.
The array of alliances is in large part the work of Soleimani himself, architect of Tehran’s growing military influence in the Middle East.
Iran-backed Shi’ite groups gained strength in Iraq after the 2003 U.S.-led invasion. Today, they have tens of thousands of fighters.
Under Soleimani’s supervision, they played a leading role in battling Islamic State, fighting as part of the Hashid Shaabi.
The strongest groups - trained, equipped and funded by Tehran - are Asaib Ahl al-Haq, Kataib Hezbollah, Harakat Hezbollah al-Nujaba and the Badr Organization.
Some of the Iran-backed Iraqi groups have fought in Syria in support of President Bashar al-Assad, another Tehran ally.
Kataib Hezbollah has been a focal point of recent tensions.
The U.S. military on Sunday mounted air strikes on its bases, accusing the group of mounting a sustained campaign against U.S. personnel since at least October.
This week, members of Iran-backed groups hurled stones at the U.S. embassy in Baghdad.
Kataib Hezbollah’s founder, Jamal Jaafar Ibrahimi, known as Abu Mahdi al-Muhandis, died in the attack that killed Soleimani.
The Iraqi government has attempted to integrate paramilitary organizations into its armed forces but the United States has said it has not seen sufficient action by Baghdad to stop attacks on U.S. forces by Iran-backed groups.
Hezbollah, meaning “Party of God”, was set up with the help from the Iranian Revolutionary Guards in 1982. In recent years, its role has expanded beyond Lebanon’s borders as it has taken part in conflicts in Iraq and Syria.
The group has tens of thousands of fighters.
Set up with the aim of fighting Israeli forces that had invaded Lebanon, Hezbollah has remained a sworn enemy of Israel, which sees it as the biggest threat at its borders.
The United States holds Hezbollah responsible for the suicide bombing that destroyed the U.S. Marine headquarters in Beirut in October 1983, killing 241 servicemen, and a suicide bombing the same year on the U.S. embassy.
Hezbollah has trained paramilitary groups in Syria and Iraq and inspired other forces such as Yemen’s Iran-allied Houthis.
Its political clout in Lebanon has grown: Hezbollah and its allies won a majority in a 2018 parliamentary election and its role in government has expanded.
Deemed a terrorist group by Washington, the group has been targeted as part of a U.S. campaign to exert pressure against Iran, with new sanctions imposed on members and businessman accused of supporting the group.
The Iran-aligned Houthi movement has been battling a Saudi-led military alliance in Yemen for almost five years.
Iran champions the Houthis as part of its regional “axis of resistance”. Saudi Arabia and its allies accuse Iran of arming and training the Houthis. But the extent of the relationship is disputed and Tehran has denied funneling weapons into Yemen.
The Houthis’ military clout includes ballistic missiles that they have used against Saudi Arabia. They deny they are Iranian proxies and say they manufacture their own weapons.
The Houthis claimed responsibility for an attack that temporarily cut more than half of Saudi oil output in September, though the United States said Iran was behind the attack.
The Houthis have an estimated 180,000-200,000 fighters under their control, according to a Chatham House report.
The Palestinian Islamist group Hamas, which rules Gaza, has a powerful armed wing thanks to Iranian financial and military support. Observers estimate the group has about 30,000 fighters and thousands of rockets.
In a November speech, Hamas Gaza chief Yehya Al-Sinwar credited Iran for the improvement of their arsenal.
The smaller Islamic Jihad group is seen by analysts as more committed to the official agenda of Iran than Hamas, but has fewer fighters and rockets.
Israel Army Radio reported that the country’s military had gone on heightened alert, fearing retaliation by Iran or its proxies after the Soleimani killing.
Additional reporting by Nidal al-Mughrabi in Gaza, Lisa Barrington in Dubai and Ahmed Aboulenein in Baghdad; Writing by Tom Perry, Editing by William Maclean