The man was carrying explosives with the apparent aim of blowing himself up inside the embassy, said Lebanese security officials on Wednesday.
"At the gate of the US embassy in Awkar, army forces
arrested a Lebanese man and a Palestinian accompanying him as they tried to bring a bomb into the embassy complex," an army statement said.
Embassy officials told Aljazeera.net that security guards at the mission's first gate were suspicious of the man, who tried to drop off a package.
They refused to say what kind of package he was carrying.
But guards suspected he was carrying explosives and immediately contacted the Lebanese army, said the source.
Embassy sources would not say what had raised the guards' suspicions about the suspect. Washington's mission in Lebanon is heavily guarded and checkpoints dot the highway around it.
Embassy staff were not evacuated from the premises.
A senior military official said the suspected bomber, a Lebanese citizen identified as Abd Mraish, was arrested by Lebanese soldiers at an army checkpoint about 500 yards from the embassy compound.
The official said that the man was carrying a kilogram of explosives in a small suitcase.
The official, speaking on condition of anonymity, refused to speculate on what the man's motives are, saying Mraish, in his 30s, was being interrogated by army officers.
An embassy spokeswoman said she was not aware of any other similar incidents in the past.