Supporters watched a live broadcast of Hezbollah’s leader, Hassan Nasrallah, at a rally in the Bekaa Valley.
BEIRUT, Lebanon — The leader of the powerful Lebanese militant group Hezbollah decisively committed his followers on Saturday to an all-out battle in Syria to defeat the rebellion against President Bashar al-Assad. He said the organization, founded to defend Lebanon and fight Israel, was entering “a completely new phase,” sending troops abroad to protect its interests.
“It is our battle, and we are up to it,” the leader, Hassan Nasrallah, declared in his most direct embrace yet of a fight in Syria that Hezbollah can no longer hide, now that dozens of its fighters have fallen in and around the strategic Syrian town of Qusayr. Outgunned Syrian rebels have held on for a week there against a frontal assault by Hezbollah and Syrian forces.
The speech signaled a significant escalation in Hezbollah’s military involvement in Syria, deeply enmeshing the group in the war across the border.
It could put new pressure on the Obama administration and on Europe, where more countries have begun pushing to list the group as a terrorist organization as the United States does. It was also likely to further inflame tensions in Lebanon, where Syria’s civil war has spilled over in explosions of sectarian violence.
Mr. Nasrallah, a shrewd political operator, appears to be calculating that the West, thrown off balance by the rise of jihadist factions among the Syrian rebels, will not jump in on the rebel side. The United States’ call for a political solution, while allowing Saudi Arabia and Qatar to arm the rebels, likewise, seems to have not shaken his confidence.
To the contrary, Mr. Assad can now head into negotiations planned for next month with a stronger hand, while the Syrian opposition is as divided and disorganized as ever.
Hezbollah “wouldn’t do this if they thought there was going to be some kind of reaction,” said Andrew J. Tabler, a Syria analyst with the Washington Institute for Near East Policy. “They’re basically calling Obama’s bluff.”
Ali Rizk, the Beirut bureau chief for Press TV, the satellite channel of Hezbollah’s patron Iran, said Mr. Nasrallah had revealed that “Hezbollah is in it militarily and is in it very deeply.”
Noting that Mr. Nasrallah, who had long equivocated about the depth of the group’s involvement, promised victory, Mr. Rizk said, “Victory means you’re in it to the very end and you’re going to go all the way. Hezbollah is going to go all the way.”
Mr. Rizk, an interpreter for Mr. Nasrallah who often speaks to Hezbollah officials, said that American hesitance might be convincing Hezbollah of what Syrian officials have believed for some time: that the United States is edging closer to the position of Russia, which wants a negotiated settlement that leaves open the possibility of a political role for Mr. Assad.
A senior administration official, however, said that despite Hezbollah’s increasing activity in Syria, the United States remained convinced that neither Mr. Assad nor the rebels were strong enough to defeat the other in battle.
“Our assessment still remains that there is not going to be a military victory,” the official said.
The official described the situation inside Syria as essentially “a standoff” and said American officials did not believe that Hezbollah’s involvement fundamentally changed the United States’ position on diplomatic efforts to remove Mr. Assad from the country.
Hezbollah’s deeper plunge into Syria does appear to aid Mr. Assad’s strategy of pushing for military gains to strengthen his negotiating position. By contrast, the fractious Syrian opposition continues to waffle on basic decisions like choosing a leader and whether to attend the peace talks.
Hezbollah has essentially become the ground assault force for the Syrian Army, an unprecedented role for the group, in the battle for Qusayr and Homs Province, which links Damascus with the government’s coastal strongholds.
“In Qusayr, the ones who are engaging on the front lines, the man-to-man firepower, that’s Hezbollah,” Mr. Rizk said. He said Hezbollah’s “infantry role” could grow, especially in border areas.
Hezbollah is also fighting near Damascus, Mr. Assad’s other top military priority, around the Sayida Zeinab shrine, a holy site particularly revered by the group’s Shiite Muslims.
But Mr. Rizk said there were limits to how much Hezbollah could turn the tide, and that Hezbollah was unlikely to send a large force toward the rebel-held northern cities of Aleppo and Idlib.
“Even some members of Hezbollah say taking back all the territory that Assad has lost is impossible,” he said.
Hezbollah’s new assertiveness could also provoke Israel. Although Israel has sought to remain neutral in Syria’s civil war, it is believed to have bombed targets in Syria three times this year to prevent the transfer of weapons to Hezbollah.
Mr. Assad has called the rebels stooges of Israel and the United States, and Mr. Nasrallah, in his speech on Saturday, echoed that theme, portraying Hezbollah’s military venture in Syria as a fight to “immunize” Lebanon from the Israeli invasion he said would surely follow if Syrian rebels prevailed.
He spoke via videotape to supporters rallying in Lebanon’s Bekaa Valley to commemorate the 13th anniversary of the end of Israel’s occupation of southern Lebanon after years of battling Hezbollah’s guerrillas, which the group considers its greatest victory.
He evoked Hezbollah’s tenacity during its 2006 war with Israel, signaling that the organization considered the fight in Syria to preserve Mr. Assad and the crucial conduit he provides for weapons from Iran, as important as its founding mission, opposing Israel and driving it out of Lebanon.
That he would equate a battle with fellow Arab Muslims in another country to the 2006 conflict, in which Israeli airstrikes leveled much of Hezbollah’s heartland in southern Lebanon and the suburbs of Beirut, is “nothing short of amazing,” Mr. Tabler said.
Sectarian passions have heated across the region as Hezbollah, a Shiite group, and Iran back a government dominated by Alawites, who follow an offshoot of Shiism, against mainly Sunni Muslim rebels.
Mr. Nasrallah, though, sought to refute accusations of sectarianism, portraying Hezbollah as acting to defend Lebanon from some of the Sunni militant groups who have joined the rebel side and who consider the Shiites infidels. “If we do not go there to fight them,” he said, “they will come here.”
In fact, he urged the Lebanese to fight out their differences in Syria and to spare Lebanon further sectarian violence.
“Whoever wants to support the opposition should go fight in Syria,” he said, “and whoever supports the regime fights there, too. Leave Tripoli alone. If both Lebanese parties are fighting in Syria, let’s fight there alone.”
That comment drew outrage on both sides of the border. Hezbollah’s political rivals here generally support its mission against Israel, but Saad Hariri, the leader of the March 14 coalition, said in a statement that “the time of exploiting Palestine, resistance and national unity has ended.”
Mr. Nasrallah, Mr. Hariri said, had doomed the resistance to “political and military suicide.”
– Hala Droubi contributed reporting from Dubai, United Arab Emirates, and Michael D. Shear from Washington.