The explosions came a few days after Prime Minister Tammam Salam formed a new cabinet to end almost 11 months of paralysis. He described Wednesday's attack as "a message by forces of terrorism to continue in their plan to spread death in Lebanon."
"We will respond to it with solidarity and our commitment to peace," he said.
Two visiting U.S. senators, Tim Kaine of Virginia and Angus King of Maine, condemned the latest spillover of violence from Syria's civil war. "We hope the formation of the government will build some trust that will enable the country" to combat terrorism, Kaine said.
Lebanese troops recently detained an alleged mastermind of similar attacks. Officials said he led them to several vehicles rigged with explosives.
One of the deadliest attacks occurred in November when two suicide attackers blew themselves outside the Iranian Embassy in Beirut, killing 23 people and wounding dozens. The Abdullah Azzam Brigades claimed responsibility.
The group's leader was captured by Lebanese authorities in December. He died in custody later in the month.
AP writers Bassem Mroue and Zeina Karam in Beirut contributed to this report.
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