CAIRO, Egypt – A prominent Lebanese journalist known for his unflinching anti-Syria columns was killed yesterday when a bomb planted inside his car exploded near the heart of downtown Beirut.

The assassination of Samir Kassir unnerved Lebanon just days after a month-long series of parliamentary elections got under way. The legislative polls have been billed as Lebanon’s first exercise in unfettered voting after 30 years of Syrian domination and civil war.

The slaying was the first attack on a prominent anti-Syria Lebanese figure since the February killing of the former prime minister Rafik Hariri. The mass demonstrations that followed Hariri’s death, bolstered by international pressure, forced Damascus to remove its soldiers from Lebanon this spring and relinquish all visible political control over Beirut. No one immediately claimed responsibility. But hours after Kassir’s death, anti-Syria politicians called for the resignation of President Lahoud of Lebanon. A faithful ally to Syria, Mr. Lahoud has managed to cling to his job despite the political earthquake that rocked Lebanon in recent months.

“The response to this new crime should be … the resignation of the president as the effective head of the security and intelligence regime,” said a statement released to reporters after the opposition meeting.

Pressure against Mr. Lahoud, whose spokesman called the attack a “grave incident,” had already been building. Key leaders such as Druze chieftain Walid Jumblatt and Saad Hariri, who has emerged as the political heir to his slain father, had called for the president’s dismissal before yesterday’s attack.

“As long as the serpent’s head is in Baabda, the assassinations will continue,” Mr. Jumblatt told Al-Arabiya TV yesterday. He was referring to Mr. Lahoud, whose presidential palace is in the suburb of Baabda.

In the months since a massive bomb killed Hariri in downtown Beirut, a series of smaller explosions have struck the city and its suburbs. At least three people were killed and dozens wounded in those attacks, which were also generally targeted at Christian neighborhoods but occurred at odd hours of the night and early morning when fewer people were about.

Yesterday’s explosion brought the violence back into the daylight hours, and into the bustling city center.

Kassir, 45, had just walked out of his home and slipped into his Alfa Romeo when the bomb went off. The blast resounded at midmorning through the streets of the relatively wealthy, predominantly Christian neighborhood of Achrifiyeh, close to the center of Beirut.

Politicians who’ve been fighting in recent months for the ouster of Syrian soldiers and the defrocking of their Lebanese allies were quick to blame Syria and its local proxies for the journalist’s death.

“The Syrian regime is responsible from head to toe for this horrific terrorist crime,” the general manger of an-Nahar newspaper, Gibran Tueni, told reporters at the scene of the explosion. An outspoken anti-Syria critic, Tueni was elected to parliament earlier this week as part of Saad Hariri’s electoral list in Beirut.

“Lebanon’s opposition should promptly close ranks anew to have every Syrian intelligence cell left behind in Lebanon ruthlessly smashed,” he said.

Damascus crumbled under intense pressure that welled up from the international community and the streets of Beirut in the weeks following the February assassination of Hariri.

The last of the Syrian soldiers withdrew from Lebanon in April, but trepidation has lingered over the role of undercover Syrian intelligence agents.

In recent years, Kassir had been one of Lebanon’s most prominent thinkers. He was a historian, professor, and author, but drew the widest notoriety for his columns in the daily an-Nahar newspaper.

“Samir was one of the very rare journalists writing in Arabic who expressed his opinions openly, especially on taboo subjects like intelligence and security services,” another prominent Lebanese columnist, Michael Young, said. “He had courage. He was not intimidated.”

The founder of a small opposition movement called the Democratic Left, Kassir was seen as a driving force in the anti-Syria street protests. In his writings, he favored subtle condemnation to over-the-top rhetoric, sneering at “Syrian patronage” and gently mocking Syrian officials.

His latest columns scolded Syria for its intransigence in an evolving region, but also turned a critical eye to his own country. In a column on Lebanon’s elections, Kassir warned readers that street protests and voting wouldn’t be enough to produce a new, independent democracy.

Having spent much of his career chronicling the bloodshed of the past, Kassir often spoke of better times ahead.

“I am sure the Lebanese deserve a better future,” Kassir told Reason magazine in 2004. “At least, they deserve to find their own way, in accordance with a rich history that cannot be reduced merely to violence. Yes, we were a laboratory for violence, but we were also, before that, a laboratory for modernity, and in some ways we still are.”