BEIRUT - A senior U.S. official denounced Hezbollah's involvement in the Syrian civil war Monday and accused the Shiite militant group of putting the interests of Iran and Syria above those of the Lebanese people.
Underscoring growing sectarian bitterness, mainly Sunni rebels vowed to "liberate" two Shiite villages they've had under siege in northern Syria if residents don't renounce President Bashar Assad's regime and force out his troops and Hezbollah fighters.
The comments by Deputy Secretary of State William Burns were the first by a high-ranking visiting U.S. official since Hezbollah helped propel Assad's troops to victory last month in the strategic town of Qusair near the Lebanese border.
Syrian troops have been building on the victory to move against rebel-held areas elsewhere in the central province of Homs and in the north. On Sunday, troops hammered rebel-held districts in Homs with artillery, tanks and warplanes, part of a government offensive launched Saturday morning.
Fighters from the powerful Iranian-backed group have joined Assad's forces in their battle to crush the rebellion, which is dominated by Sunnis.
"Despite its membership in the Lebanese government, Hezbollah has decided to put its own interests and those of its foreign backers above those of the Lebanese people," Burns told reporters as he wrapped up a two-day visit Monday to Lebanon.
"That intervention may be in Hezbollah's interests, it may be in the interest of Iran, it may be in the interest of Bashar Assad, but it is not in the interest of Lebanon or the Lebanese people," Burns said.
He added that the U.S. condemned "in the strongest terms" Hezbollah's actions in Syria and said they "place the future of Lebanon at risk."
The U.S. considers Hezbollah a terrorist organization.
The group's open participation in the war has helped fan sectarian hatred in Lebanon and across the region. Its fighters were instrumental in helping Assad's troops capture Qusair, and activists say Hezbollah members are fighting in several locations in Syria.
Hezbollah leaders and Assad, however, deny those reports. Assad said in a recent interview that Hezbollah's involvement was restricted to Qusair because of its proximity to Lebanon.
The group, however, is known to be fighting alongside troops in the predominantly Shiite villages of Nubul and Zahra in the northern province of Aleppo, besieged by rebels for a year.
On Monday, rebels fighting in Aleppo vowed to attack the two villages if their residents do not renounce the Assad regime.
In a YouTube video, a group of rebels who identified themselves as being from a joint brigade that fought in Qusair demanded that Assad loyalists in the town hand over Assad militiamen and Hezbollah fighters along with their weapons and release rebels they hold prisoner.
"After that, the siege will be lifted and food and medicine will enter, and normal life will return," one rebel says. "But if there is no answer, there will be a large military attack on the two villages. You have been warned."
The video, confirmed by an activist in Aleppo, underscores the growing sectarian nature of the civil war, which has killed more than 100,000 people in two years, according to activists.
The conflict reflects the struggle for influence between Shiite Iran, which supports Assad, and major Sunni power Saudi Arabia, backed by smaller Gulf Arab states, such as Qatar, and non-Arab Turkey, which support the rebels.
At home, Assad draws support largely from Syria's minorities, including fellow Alawites - followers of an offshoot of Shiite Islam - as well as Christians and Shiites. His other foreign backers include Russia and China.
Rising tensions between Sunnis and Shiites linked to the Syrian conflict has sparked deadly street fighting between the rival sects in Lebanese cities.
Last week, sectarian tensions drew Lebanon's weak army into the fray. Eighteen soldiers were killed in two days of fighting in the southern city of Sidon between the army and supporters of a hard-line Sunni sheik whose popularity has soared by tapping into the frustrations of many Lebanese who resent the influence that Shiites have gained in government via Hezbollah.
"At a time of regional tumult and domestic uncertainty, it is deeply in the self- interest of all Lebanese to exercise restraint and respect for Lebanon's stability and security," Burns said.
Burns said he conveyed to President Michel Suleiman "our condolences and deepest sympathies for members of the Lebanese Armed Forces and innocent civilians" killed and injured in Sidon.
Burns also criticized a Lebanese government decision to postpone scheduled parliament elections last month, saying it undermines the people's faith in their government and shakes the confidence of the international community in the country's institutions.
In other violence in Syria, the state-run news agency SANA said three people were killed and 18 injured in a suicide bombing near the cultural center in the town of Sabboura. Two suicide bombers detonated a pickup truck packed with about 1.5 tons of explosives in front of the cultural center, it said.
Associated Press writer Diaa Hadid contributed to this report.