WASHINGTON (AP) — With little official information to guide them, members of Congress said Monday there was scant or no doubt that the deadly Boston Marathon explosions were acts of terrorism and vowed to bring anyone responsible to justice.

"We just don't know whether it's foreign or domestic," said Rep. Michael McCaul, R-Texas, chairman of the House Committee on Homeland Security.

"My understanding is that it's a terrorist incident," Sen. Dianne Feinstein told reporters, saying she had been in contact with U.S. intelligence agencies. Feinstein, who chairs the Senate Intelligence Committee, said intelligence officials reported no advance warning that "there was an attack on the way."

Sen. Saxby Chambliss of Georgia, the senior Republican on the panel, issued a written statement that said, "As the evidence mounts that this was a terrorist attack, our intelligence and law enforcement agencies must do whatever is necessary to find and interrogate those responsible so we can prevent similar attacks."

The remarks stood in contrast to President Barack Obama's own brief statement at the White House, where he made no mention of terrorists or terrorism as a possible cause of the bombings.

Two other members of the intelligence panel, Sens. Susan Collins, R-Maine, and Angus King, I-Maine, said that based on initial news reports that "multiple improvised explosive devices may have been involved at this high profile national event bear the hallmarks of a terrorist attack."

McCaul spoke with reporters in the House, and said he had talked with federal and state officials in the hours since the attack that he said "had all the hallmarks of terrorism."

Members of the House and Senate intelligence committees said they expected to be briefed on the attack on Tuesday.

Majority Leader Harry Reid said on the Senate floor that Obama had spoken with officials in Massachusetts and "pledged every federal resource available ... to bring justice to the perpetrators...."

House Democratic Leader Nancy Pelosi said "we will ensure that justice will be done" as the casualty toll mounted in explosions blamed for at least two deaths and dozens of injuries.

Lawmakers in both houses marked the bombings with moments of silence.

Reid led the Senate in a brief pause, and officials said Speaker John Boehner intended to do the same when the House convened later Monday.

In a written statement, Boehner said: "This is a terrible day for all Americans, but we will carry on in the American spirit, and come together with grace and strength."

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Associated Press writers Andrew Taylor, Donna Cassata, Richard Lardner and Andrew Miga contributed to this report.

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(Photo: AP Photo/The Daily Free Press, Kenshin Okubo)