A suicide bombing at a checkpoint on the Beirut-Damascus highway killed one person Friday just before a convoy passed carrying a top Lebanese security official seen as close to Hezbollah.
The attack came shortly after the security forces raided a hotel in central Beirut and detained 17 people, an official statement said, although it was unclear how the arrests were linked to the blast.
One person was killed and 32 were wounded in the Dahr al-Baydar suicide attack east of Beirut, the national News Agency (NNA) reported the health ministry as saying.
An official said the dead man was a member of the Internal Security Forces (ISF).
Friday's attack was the first inside Lebanon since March. As war has raged in neighbouring Syria over the past three years, scores of people have been killed in a wave of bomb attacks.
General Abbas Ibrahim, who heads the powerful General Security Agency, said the attack at Dahr al-Baydar which narrowly missed his convoy was linked to recent violence in Iraq.
"The whole of Lebanon is a target," Ibrahim told a private Lebanese television channel, adding that he "constantly" receives threats, and those he has received recently have been particularly "worrying".
However, he refused to say whether he thought he was the target of the attack.
"The interior minister (Nohad al-Mashnuq) has already said that what is happening in Iraq will have a catastrophic impact on Lebanon... and this is true. We are preparing ourselves for such a phase," Ibrahim told LBC.
Jihadists from the Islamic State of Iraq and the Levant (ISIL) have spearheaded a Sunni militant offensive in Iraq that has seen Mosul, the second city, fall from government control over the past week.
"What happens in any country in the region will necessarily impact the whole of the region," Ibrahim said.
- Role in prisoner swap -
Signup to our newsletter and follow us on Facebook and Twitter!
Ibrahim is seen as close to Lebanon's Shiite movement Hezbollah and its ally Damascus. He played a key role in an exchange of prisoners held by President Bashar al-Assad's regime and a group of nuns held by Syrian rebels.
After Friday's blast, chief military prosecutor Saqr Saqr told reporters at the scene of the attack that some 25 to 30 kilos of explosives had been detonated.
Mashnuq later told reporters the suicide attacker "had a Syrian accent", and that "trusted Western and international agencies" had said Lebanon "is under threat" of possible new attacks.
During the three years of the Syria conflict, Lebanon has suffered a wave of attacks, many of which targeted areas dominated by Hezbollah and were claimed by extremist Sunni groups.
The ISF said it detained on Friday 17 people "who hold various nationalities" from a Beirut hotel in the busy Hamra district.
The ISF statement also said its members had been monitoring the vehicle driven by the man who eventually carried out the suicide attack.
As it approached Beirut, the driver turned back after realising he was being tailed, and he then set off the explosives when he was stopped at the checkpoint.
The ISF issued a picture of the suspected bomber and appealed for information.
After the bombing, security forces and the army closed off several roads in the capital and set up barricades around the interior ministry and other key locations.
The US embassy and the United Nations condemned the blast, while the French embassy asked citizens based across Lebanon to avoid unnecessary travel on Friday.
Security in fragile Lebanon had improved after many months of frequent explosions and gun battles in flashpoint areas.
Most blasts had targeted Hezbollah-dominated areas, and were claimed by Sunni extremists who blamed the Shiite movement for sending thousands of fighters into Syria to support Assad's regime.
Lebanon remains deeply divided over the conflict in its larger neighbour, with Hezbollah and its allies backing Assad and the Sunni-led March 14 bloc supporting the revolt against him.
Lebanon was dominated by Damascus for nearly 30 years until a massive bomb attack killed former prime minister Rafiq Hariri in 2005.