BEIRUT (AP) -- Hezbollah was pulled more deeply into Syria's civil war as 28 guerrillas from the Lebanese Shiite militant group were killed and dozens more wounded while fighting rebels, Syria activists said Monday.
The intense battle drove rebels from large parts of the town of Qusair, part of a withering government offensive aimed at securing a strategic land corridor from Damascus to the Mediterranean coast.
Hezbollah-affiliated hospitals in Lebanon urged blood donations through mosque loudspeakers and ambulances raced along the Damascus road in a stark indication of the group's increasingly prominent role in Syria.
The overt Hezbollah involvement -- several funerals for group members were held Monday in Lebanon -- edges the war further into a regional sectarian conflict pitting the Middle East's Iranian-backed Shiite axis against Sunnis.
It also raised tensions considerably in Lebanon, where Hezbollah has come under harsh criticism for its involvement in the civil war next door.
A staunch ally of Syrian President Bashar Assad, Hezbollah is heavily invested in the survival of the Damascus regime and is known to have sent fighters to aid government forces. The Iranian-backed group's growing role in the conflict also points to the deeply sectarian nature of the war in Syria, in which a rebellion driven by the country's Sunni majority seeks to overthrow a regime dominated by Assad's Alawite sect, an offshoot of Shiite Islam.
Clashes continued for the second day in the northern city of Tripoli, Lebanon, where Sunnis and Alawites battled in a direct spillover from the fighting in Qusair.
The Britain-based Syrian Observatory for Human Rights, which tracks Syria's civil war, said that more than 70 Hezbollah fighters have also been wounded in the fighting around Qusair.
The White House said President Barack Obama telephoned Lebanon's president and expressed concern about Hezbollah's "active and growing role in Syria, fighting on behalf of the Assad regime, which is counter to the Lebanese government's policies."
More than 70,000 people have been killed and several million displaced since the uprising against Assad erupted in March 2011 and escalated into a civil war. The Syrian government and Hezbollah deny there is an uprising in Syria, portraying the war as a foreign-backed conspiracy driven by Israel, the U.S. and its gulf Arab allies.
In addition to the Hezbollah involvement, Iraqi Shiite fighters have for months trickled into Syria. Their relatives say they are drawn by a sense of religious duty to protect Shiite Muslim shrines in Syria.
Hezbollah leader Sheik Hassan Nasrallah said in a recent speech that his fighters had a duty to protect the shrines. He also claims that supporters of the group were fighting in Shiite villages near the Lebanon border against the rebels, saying it was in self-defense.
The Observatory, which relies on a network of activists inside Syria, cited unidentified "sources close to the militant group" for its Hezbollah death toll Monday. It said at least 50 Syrian rebels also were killed in the battle for Qusair on Sunday.
Qusair has been the target of a Syrian government offensive in recent weeks, and the surrounding countryside has been engulfed in fighting as regime troops backed by Hezbollah fighters seized villages while closing in on Qusair itself.
The intensity of the fighting reflects the importance that both sides attach to the area. In the regime's calculations, Qusair is strategically located between Damascus and the Alawite heartland near the Mediterranean. For the rebels, overwhelmingly Sunni Qusair has served as a conduit for shipments of weapons and supplies smuggled from Lebanon to opposition fighters inside Syria.
A Lebanese official close to Hezbollah told The Associated Press that the death toll figures were "exaggerated." He added, however, that 14 Hezbollah members from southern Lebanon were killed in the fighting Sunday, adding that some of the fighters' bodies were still in Syria. He spoke on condition of anonymity for fear of reprisals from Hezbollah, which maintains a shroud of secrecy on its security operations.
Evidence of the group's heavy involvement in Syria was on full display Monday.
In the town of Nabi Sheet in eastern Lebanon's Bekaa Valley, a Hezbollah stronghold, about 2,000 people attended the funeral of Hassan Shukur, an 18-year-old Hezbollah fighter.
Hezbollah comrades fired in the air in mourning and played the group's funeral march as they carried Shukur's coffin draped in a yellow Hezbollah flag through the streets at his funeral attended by senior members of the group.
"We will fight in all of Syria because we are fighting the Israeli enemy," said Sheik Mohammed Yazbeck, a member of Hezbollah's highest decision-making body, the Shura Council.