But the former information minister said he had been the victim of entrapment because he was not aware that his co-conspirator was a Lebanese security services informer.
Samaha, who was also once an adviser to Syria's President Bashar al-Assad, made the surprise admission during the first session of his long-delayed trial before a military tribunal.
"I received from the Syrians USD 170,000 inside a bag... and put it in the boot of my car with the explosives," he said.
"I fell into the trap laid by Milad Kfouri, who was tied to the intelligence services," Samaha said.
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"True, I made a mistake, but I wanted to avoid sectarian strife."
Samaha's lawyer Rana Azoury confirmed that the former minister had acknowledged transporting the explosives under pressure from Kfouri.
"Samaha explained that he fell into a trap laid by the Lebanese intelligence services through an intermediary... Milad Kfouri," she said.
The explosions were intended to force the closure of the border and stop the passage of Lebanese fighters who wanted to join rebels fighting against the Syrian regime, he said.
"Under Lebanese law, if you acted because of the encouragement of an agent provocateur, that is exculpatory and a legitimate self-defence," Azoury said in explaining Samaha's testimony.
Samaha has been under arrest since August 2012 over allegations that he and Syrian security services chief Ali Mamluk transported explosives and planned attacks and assassinations of political and religious figures in Lebanon.