Hezbollah is expanding its reach into Middle East

• Hezbollah is a Shiite Muslim faction known chiefly for its wars against Israel
• Hezbollah is fighting in Syria alongside Iran%2C the largest Shiite nation in the Middle East
• Hezbollah has sent hundreds of fighters from Lebanon to Syria to fight Muslims

A previous version of this article misattributed quotes.

BEIRUT — U.S.-designated terror group Hezbollah is expanding networks and deployment of fighters from Lebanon to the entire Middle East as part of its deepening alliance with Iran, say analysts.

The latest sign comes in Syria, where Hezbollah leader Hassan Nasrallah has justified intervention as a battle he says is part of a region-wide war of Sunni Muslims against Shiite Muslims.

"Nasrallah used very sectarian language to justify the organization's role in Syria," said Nadim Shehadi, a researcher at the think tank Chatham House, referring to the head of Hezbollah.

Both Hezbollah and Iran are dominated by Shiite Muslims; Sunni Muslims control many countries that are U.S. allies such as Saudi Arabia. The Sunni-Shiite split goes back to almost the beginning of Islam but the two branches coexist in many Middle East nations where civil unrest between them is always a threat.

Hezbollah is chiefly known for its wars against Israel from its base in southern Lebanon and for its numerous terror attacks against Americans and Jews. But in a first, Hezbollah has sent hundreds of fighters from Lebanon to another country to fight not against infidels but fellow Muslims.

Facing criticism for the departure in targets, Nasrallah has said Syria is about helping an ally of Shiite Muslims from defeat by Sunni Muslims, Americans and Israelis. Nasrallah's reference to the Islamic schism could open up new fronts in Arab nations like Bahrain and Iraq where Sunnis and Shiites reside together in often uneasy circumstances.

That Hezbollah is fighting in Syria alongside Iran, the largest Shiite nation in the Middle East, only makes the Hezbollah threat more fearful to Sunni-dominated nations, says Shehadi, like U.S. allies Bahrain and Yemen.

"By sending it combatants to Syria to fight insurgents, Hezbollah is using its Lebanese Shiite constituency for its regional war," he says.

In Syria, the majority of Muslims are Sunnis. But the Syrian government has been controlled for decades by a dictatorship dominated by a Shiite Muslim sect called Alawites. In 2011, Sunnis in Syria held peaceful protests in some cities to demand democratic reforms giving them more say. Alawite dictator Bashar Assad responded by unleashing his military, blowing up whole neighborhoods from the air and strafing civilian populations from the ground.

More than 100,000 people have died in the conflict, says the United Nations, and 2 million people have fled the country. Hezbollah has been sending hundreds of its militants to Syria to fight the Sunnis alongside Iranian and Syrian soldiers.

Abou Ali is a Hezbollah fighter who recently returned from deployment in Damascus, the capital of Syria. He believes in what Nasrallah is saying about the conflict.

"By waging war on Syria they are targeting Hezbollah," he said of the Sunnis, whom he insists are allied with non-Muslim nations. "If someone comes to your house to kill you, don't you have the right to defend yourself?"

But some Lebanese Shiites are uncomfortable with the development.

"What are we doing invading another country to fight its people? We are killing other Muslims," said Dahieh resident Abou Hassan. "The war in Syria is not right. It will not be in favor of the Shiites in Lebanon."

With the Arab Spring, Hezbollah activity became more acute in other Arab countries stretching from Yemen to Bahrain.

Examples abound. In an interview published recently in Arab daily al-Hayat, Yemeni Foreign Minister Abu Bakr al-Qirbi expressed concern over former South Yemen President Ali Salem al-Baidh's relations with Hezbollah, which is currently providing protection for him in Lebanon.

Early this year, a cargo ship loaded with highly sophisticated weapons, including surface-to-air missiles, was discovered en route to areas controlled by the Shiite Houthi militants, according to the Yemen Post.

"The organization's activity in Yemen is not new and was pointed out by CIA director John Brannan in a previous conference," said Matt Levitt, director of the Stein Program on Counterterrorism and Intelligence at the Washington Institute for Near East Policy and author of Hezbollah: The Global Footprint of Lebanon's Party of God. "Iran is sending weapons to the Houthi via Hezbollah."

In addition, in 2011 Bahrain filed a report with the U.N. Secretary General alleging that Shiite Bahraini opposition members who staged an uprising against the Sunni-ruled government were being trained in Hezbollah camps in Lebanon and Iran. The reports are denied by Hezbollah and the Bahraini opposition.

Bahrain is trying to neutralize Hezbollah's influence by banning the group's al-Manar news website and prohibiting opposition groups from maintaining links with the organization.

"There is a history of Hezbollah activity in Bahrain, where a Bahraini Hezbollah branch was set up and there are radicals who have spent time in Lebanon, but it is unclear how much credence to give Bahrain's allegations against Hezbollah," Levitt said.

It has a history elsewhere, too.

The group provided money, training and expertise in explosives to Hamas, the terrorist group that controls Gaza, during the Palestinian Intifada in 2000, says Nicholas Blanford, author of Warriors of God: Inside Hezbollah's Thirty-Year Struggle Against Israel.

In the Iraq War, Hezbollah trained Shiite paramilitary squads, such as Kataeb Hezbollah and Assayib Ahl al Haqq, at the request of Iran, he said.

"If Hezbollah today plays a regional role, it is at the behest of Iran, and it is not a role it aspires to," Blanford said.

Shehadi says Hezbollah is now facing problems aligning its role as a Lebanese political party with the goals of its Iranian backers, "but it is willing to sacrifice its constituency to satisfy Iranian interests," he said. "It is feeding sheep to the slaughter."