Hezbollah leader Hassan Nasrallah, a staunch ally of Damascus, has denied that his group received chemical weapons from Syria.
Last month, members of the opposition Syrian National Coalition group accused President Bashar al-Assad of transferring chemical weapons to the Lebanese Shia group to avoid inspection after agreeing to put them under international control.
"This accusation is truly laughable," Nasrallah said on Monday in a televised speech.
"We understand the dimensions and background of these accusations, and these have dangerous consequences for Lebanon.
Syria has agreed to give up its chemical weapons under a plan agreed by the United States and Russia after Western powers blamed Assad's government for a chemical attack that killed hundreds of people in a Damascus suburb last month.
Israel's commander on the frontier with Syria, Major-General Yair Golan, said this month that Hezbollah sought precision ground-to-ground rockets, anti-aircraft and anti-ship missiles from Syria in return for helping Assad, but "as far as we can tell" it did not want his chemical weapons.
Nasrallah urged supporters of Syrian rebel forces to "review their positions" and back a political settlement.
The intervention of Hezbollah fighters in Syria has raised fears among some Lebanese that the small Mediterranean country could become engulfed by its much larger neighbour's conflict, which has killed over 100,000 people.
Rocket and bomb attacks have hit Hezbollah strongholds in the Bekaa Valley and in the capital - a car bomb killed at least 22 people in southern Beirut last month.
Nasrallah accused a radical Sunni group "working in the framework of the Syrian opposition" of carrying out the attack. He said the group had Lebanese and Syrian members but did not name it.
Earlier on Monday, Lebanese security forces replaced Hezbollah forces at checkpoints in the southern suburb which the group had set up after the car bomb.
Nasrallah said the group welcomed the deployment of the security forces and urged residents to cooperate with them.