WASHINGTON – As Iraqis yesterday suffered the deadliest explosion since the fall of Saddam Hussein, the country’s interim government and the American military were saying they see an increasing Syrian role in the insurgency.

Ambulances and volunteers carted away the wounded and dead in Hillah after a powerful car bomb killed at least 115 nearby shoppers at a market and new recruits lining up for medical tests to join Iraq’s national guard in the largely Shiite city south of Baghdad. The Associated Press reported that the blast wounded another 132 people.

“Empty shoes and sandals of those killed or wounded were thrown into a corner. Scorch marks infused with blood covered the clinic’s walls. Morgue workers unloaded plastic body bags from pickup trucks as weeping relatives looked on,” the AP reported. “Some of the victims were shoppers or vendors from a nearby outdoor street market selling produce, sandwiches, and other food. But most were recruits waiting outside the clinic.”

While neither Iraqi nor American officials pinned blame for the suicide bomb blast on the world’s last remaining Baathist dictatorship, a consensus has emerged that much of the insurgency today is being planned on Syrian soil.

“The improvised explosive devices are at the same level and appear to be targeting Iraqis more. These kinds of things are organized and operated by people mostly in Syria. The insurgency has been allowed to set up headquarters by the Syrian government,” Senator Brownback, a Republican of Kansas, told The New York Sun en route from Iraq to Washington yesterday. He said this was the judgment both of senior military commanders and the interim prime minister, Iyad Allawi.

Mr. Brownback called the attack yesterday “horrific,” adding, “I’m hopeful this has the impact of pulling the country together rather than driving it apart. There is an interesting thing happening. Iraqi television is now broadcasting interviews of insurgents,” he said. The insurgents “did this for pay. This was not about Baathism or occupation, this was about mercenaries. This is having an effect on public opinion,” he said.

Syria has come under extraordinary pressure in the time since the assassination of Lebanese politician and developer Rafik Hariri on February 14, which Lebanon’s opposition has blamed on Damascus. The assassination has energized the population, leading to the collapse yesterday of the pro-Syrian government in Beirut. Less than 48 hours after Hariri’s murder, the State Department recalled its ambassador from the Syrian capital.

On Sunday, Iraqi officials announced that Bashar al-Assad’s regime had helped in the apprehension of Saddam’s half-brother, Sabawi Ibrahim al-Hassan, a leader of the Iraqi insurgency. For months, the Syrians have chalked up any presence of Iraqi insurgents on their territory to poor border security, insisting that their intelligence services and banks have not supported what they have described as a grassroots movement. Indeed, in October, Britain and America pledged to sell the Syrians advanced equipment to better secure the border, according to two State Department officials and one member of the House of Representatives.

Recent analyses from the Treasury Department and American intelligence agencies, however, estimate that Syrian banks are funneling hundreds of millions, if not billions, to former Baathist officials plotting attacks on Americans and Iraqis.

“We need to really confront Syria at this point in time,” Mr. Brownback said yesterday. “We need to get more aggressive in helping organize civil society groups to oppose the regime.” He told the Sun he was eyeing new legislation to set aside monies for civil society organizations inside Syria, similar to the funding he has secured in previous years for the Iranian opposition. To date, however, the State Department has not made grants to pro-democracy organizations in Iran. Mr. Brownback sits on the Senate appropriations subcommittee that oversees foreign assistance.

On her way to a London conference on Palestinian reform, Secretary of State Rice commented on Israeli allegations that Syria’s fingerprints were on the Friday suicide attack in Tel Aviv. “We don’t have any confirmation of who, of whether there was foreign involvement,” Ms. Rice said yesterday. “But, obviously, the involvement of the Syrians with terrorists and terrorism is well known and it’s been one of the most important barriers to improved relations with the Syrians on the part of the United States. We’ve said many, many times that the Syrians cannot have it both ways, talk about an important peace process and still support rejectionist elements who are intentional – who intend to blow up that process or to frustrate that process.”

The Syrian leader, Bashar al-Assad, told the Italian newspaper La Repubblica yesterday that he fears an American invasion of his country. “The language used by the White House indicates a campaign similar to the one that preceded the attack on Iraq,” he said. At another point he said, “We are essential for the peace process, for Iraq. Look, perhaps one day the Americans will come and knock on our door.”

The White House has yet to announce the next round of sanctions required under the Syria Accountability Act, which the president signed in 2003.