Beirut, Lebanon (CNN) -- A top Lebanese intelligence official was on his way to discuss a recent threat allegedly linked to Syria when he was assassinated last week, a lawmaker told CNN on Monday.
A car bomb killed Brig. Gen. Wissam al-Hassan and two others Friday, 30 minutes before he was to meet with Lebanese lawmaker Amar Houri to discuss a threatening text message sent to the lawmaker from a Syrian phone number, according to parliamentarian Ahmad Fatfat.
Similar threats had been sent via text message to three other lawmakers, including Fatfat, although they did not realize it until after al-Hassan's assassination, Fatfat said. All four are members of Lebanon's Future Movement, the largest member of the vocally anti-Syrian March 14 political coalition led by Saad Hariri.
After al-Hassan's assassination, Fatfat said he and his colleagues received another text from a similar phone number threatening further killings: "Congratulations, the countdown has started," the text read. "One of ten."
Al-Hassan, who was killed along with a bodyguard and a bystander, was an icon among many fellow Sunni Muslims -- including those aligned with Hariri's opposition coalition -- for his leadership and efforts in rooting out those responsible for targeted killings in Lebanon.
But as much as he was loved by some, he angered others -- especially those backing Syrian President Bashar al-Assad and many affiliated with Hezbollah, the Shiite militant and political movement that has a prominent role in Lebanon's government. The U.S. government labels it a terrorist organization. However, Hezbollah is widely popular with many of Lebanon's Shiite Muslims.
The lawmakers had told al-Hassan about the threatening texts they had received before Friday's attack, and al-Hassan had agreed to meet with one of them Friday to discuss the details.
U.S. State Department spokesman Mark Toner said Monday that an FBI team will be sent to Lebanon to assist in the investigation into al-Hassan's death.
Since the assassination, sporadic fighting has erupted across Lebanon, threatening to plunge the country into chaos and raising fears that it could be drawn into the bloody 19-month-old civil war in neighboring Syria.
After al-Hassan's funeral Sunday, angry protesters clashed with security forces and rushed toward the prime minister's office, calling for his dismissal.
By midday Monday, at least three people had been killed in the northern city of Tripoli, while another person was killed in the southern city of Sidon, and another killed in Beirut, Lebanon's official National News Agency reported. More than two dozen people were injured nationwide.
Amid the unrest, the youth wing of the March 14 coalition called for a peaceful rally in Beirut's Martyrs' Square on Monday evening. The March 14 movement is an anti-Syrian coalition that emerged after the 2005 assassination of former Prime Minister Rafik Hariri. His son, Saad, leads the coalition.
Syria has condemned the attack but that hasn't stopped accusations it is behind Friday's killing, which marked the country's highest-profile assassination in more than seven years.
The United States has also condemned the attack and vowed to assist in investigating the bombing.
CNN's Saad Abedine contributed to this report.