President Barack Obama's top advisers were to make their case for limited military strikes against Syria to the full Senate on Saturday, presenting evidence of a chemical weapons attack last week that the White House says killed more than 1,400 people.
Obama has broad legal powers to take military action. While he has said he has not made a final decision, he has made it clear that he believes the United States must do something to hold the Syrian government accountable for the attack.
But U.S. lawmakers have pushed for more information about Obama's intentions in Syria, with many expressing reservations about the cost and impact of potential strikes.
On Saturday afternoon, top national security officials will hold unclassified conference calls with the Senate Democratic Caucus as well as the Senate Republican Conference, a White House official said.
Secretary of State John Kerry and Defense Secretary Chuck Hagel will participate, as well as Director of National Intelligence James Clapper, Obama's National Security Adviser Susan Rice, and Admiral James Winnefeld, vice chairman of the Joint Chiefs of Staff.
The discussions come a day after the White House released an unclassified intelligence assessment that said the government had "high confidence" that the Syrian government was responsible for an August 21 chemical weapons attacks in a dozen neighborhoods outside Damascus that killed at least 1,429 civilians, a third of them children.
Obama and Kerry said the United States could not ignore the attack, but have not said whether or when they plan to strike.
"So the primary question is really no longer, what do we know? The question is, what are we - we collectively - what are we in the world going do about it?" Kerry said in a televised address on Friday.
Protracted and expensive wars in Afghanistan and Iraq have left Americans reluctant to get involved in Middle Eastern conflicts.
Most Americans do not want the United States to intervene in Syria. A Reuters/Ipsos poll taken this week showed only 20 percent believe the United States should take action, but that was up from 9 percent last week.
Obama and Kerry have said they recognize Americans are tired of war, and have emphasized that they do not plan an "open-ended" response and will not send U.S. troops into the country.
Late on Friday, defense officials said a sixth U.S. warship has now been positioned in the eastern Mediterranean, near five U.S. destroyers armed with cruise missiles that could soon be directed against Syria as part of a "limited, precise" strike.
However, the officials stressed that the ship, with several hundred U.S. Marines on board, was in the region for a different reason and was being kept there only as a precaution. There were no plans to put Marines on the ground as part of any military action against Syria, they said.
Some lawmakers have said Obama should seek backing for the strike with a vote in Congress. "The American people I think really deserve that debate," said Barbara Lee, a California Democrat in the House of Representatives, in an interview with CNN.