(CNN) — Mohamad Chatah, a former Lebanese finance minister and ambassador to the United States, was killed Friday when a car bomb struck his convoy in downtown Beirut, Lebanon's National News Agency reported.
Five others were killed and 71 were wounded, Lebanon's health ministry said. Cars were burned beyond recognition as a wall of flames and thick black smoke shot up from the blast site.
Chatah's bodyguard, Mohammed Badr, was among those killed, the news agency said.
No one has claimed responsibility for the attack.
Chatah's last tweet, posted about an hour before his death, talked about Hezbollah, the Lebanese-based Shiite militant group with which Chatah was at odds.
"#Hezbollah is pressing hard to be granted similar powers in security & foreign policy matters that Syria exercised in Lebanon for 15 yrs," Chatah tweeted.
Chatah was known as a staunch critic of Syrian President Bashar al-Assad, whom he accused of meddling in Lebanon's internal affairs. Hezbollah has sent fighters to help al-Assad's forces in the Syrian civil war.
"A united and peaceful Syria ruled by Assad is simply not possible anymore. It has been like that for some time," Chatah wrote in his last blog post. "The status quo ante cannot be restored. Iran and Hezbollah realize this more than anyone else."
More than 100,000 people have been killed in Syria, where al-Assad's forces are battling rebels seeking an end to his family's four-decade dynasty. Al-Assad and the core of his regime are Alawites, members of an offshoot of Shia Islam, but most Syrians and a large portion of the rebels are Sunni.
The war has spilled across the border into Lebanon. Dozens have been killed there in largely sectarian violence, including dual bombings last month that left 23 dead in Beirut.
The Abdullah Azzam Brigades, a Sunni jihadist group linked to al Qaeda, claimed responsibility for those bombings. The group warned more attacks would come unless Hezbollah stopped sending fighters to support Syrian regime forces.
A diverse career
Chatah graduated from American University in Beirut and was Lebanon's ambassador to the United States from 1997 to 1999, according to his blog. Chatah also was a senior adviser for former Prime Minister Saad Hariri and was the finance minister in former Prime Minister Fouad Siniora's Cabinet in 2008 and 2009.
Hariri issued a statement Friday condemning the killing, calling it "yet another terrorist message sent to us, we the free men of Lebanon in the Future Movement and March 14 coalition."
Hariri's "March 14 coalition" is a pro-Western, Sunni-dominated bloc. It takes its name from the day in 2005 when thousands gathered in Beirut a month after the assassination of Hariri's father, former Prime Minister Rafik Hariri, to demand an end to the Syrian occupation of Lebanon.
Shortly before Lebanon's presidential election in 2007, Chatah decried the violence plaguing Lebanon ahead of the country's elections.
"We're still witnessing killings, explosions targeting those people who really were after one thing -- they were after the independence of Lebanon, restoration of its sovereignty, re-establishment of state authority, and having a normal life. And for that, they're paying with their lives," Chatah said.
On Friday, Lebanese Prime Minister Najib Mikati posted a tweet saying he is calling off his vacation and heading back to Lebanon.
"I condemn this assassination, which targeted a political, an academic, a moderate and an upscale figure who always believed in dialogue and the language of reason, logic and the right to have a different opinion," Mikati said.
Chatah was married and had two children.
His death comes 20 days before the U.N.-backed Special Tribunal for Lebanon begins the trial of four Hezbollah suspects over the 2005 assassination of Rafik Hariri. Like Chatah, Hariri was also killed in a car bombing.
CNN's Nada Husseini contributed to this report.