1:00 p.m. ET -- Royce asks what other governments are telling the U.S. in terms of their support.
Kerry says the U.S. has reached out to over 100 countries. "Fifty-three countries or organizations have acknowledged that chemical weapons were used, and 37 have said so publicly," he says. "That will grow as the evidence we released yesterday becomes more prevalent."
He says he'll meet with 28 foreign ministers of Europe on Saturday. In addition, 31 countries or organizations have stated publicly the Assad regime was responsible for this attack, Kerry says. Thirty-four countries or organizations have indicated that if the allegations turn out to be true, they would support some form of action against Syria, Kerry adds.
"A number of countries in the region, friends of ours, have offered to be part of this operation," he says, though adding that the U.S. military believes it has more offers of help than it needs to carry out the mission.
12:55 p.m. ET -- Hagel: "The Assad regime, under increasing pressure by the Syrian opposition, could feel empowered to carry out even more devastating chemical weapons attacks. Chemical weapons make no distinction between combatants and innocent civilians, and inflict the worst kind of indiscriminate suffering, as we have recently seen."
12:53 p.m. ET -- Hagel: "General Dempsey and I have assured the President that U.S. forces will be ready to act whenever the President gives the order. We are also working with our allies and partners in this effort. Key partners, including France, Turkey, Saudi Arabia, the United Arab Emirates, and other friends in the region, have assured us of their strong support for U.S. action."
Some Western governments are preparing for the possibility of a strike on Syria following reports of a suspected chemical attack on a Damascus suburb. While many options are being considered, some officials say limited missile strikes are a likely possibility.
12:48 p.m. ET - Hagel: "As a former Senator and member of this committee, I welcome this debate and I strongly support President Obama's decision to seek congressional authorization for the use of force in Syria."
12:47 p.m. ET -- Kerry: "This is not the time for armchair isolationism. This is not the time to be spectators to a slaughter....Neither our country nor our conscience can afford the cost of silence."
12:42 p.m. ET -- CNN Chief Congressional Correspondent Dana Bash reports the Senate Foreign Relations Committee will mark up the resolution at 2 p.m. ET. Sen. John McCain plans to propose an amendment.
12:42 p.m. ET -- Hagel and Dempsey just arrived at the House hearing, while Kerry is still giving his opening statements. Hagel and Dempsey were giving a classified briefing to the Senate Armed Services Committee this morning.
12:39 p.m. ET -- "The risk of not acting is greater than the risk of acting," Kerry says. He again says he can guarantee "a far greater likelihood of conflict in the future" if the U.S. doesn't act. "We know Assad will read our silence, our unwillingness to act, as a signal that he can use his weapons with impunity."
Kerry adds the U.S. intelligence community can prove Assad has used chemical weapons at least 11 times.
A former U.N. weapons inspector explained Tuesday to CNN how "signatures of sarin" can be identified and how reliable testing and sampling can be.
12:34 p.m. ET -- John Kerry reiterates the argument that the "red line" on chemical weapons was not just drawn by Obama, but by Congress, as well. Kerry says the world is watching to see whether "the United States will consent through silence." Obama said the same thing earlier in the day in Sweden.
12:31 p.m. ET - John Kerry: "I can tell you beyond a reasonable doubt the evidence proves the Assad regime prepared this attack."
Sarin--a clear, tasteless and odorless nerve agent--is one of the most toxic chemical weapons. Dr. Sanjay Gupta, CNN's chief medical correspondent, said a fraction of an ounce of sarin on a person's skin could be fatal.
"It can be absorbed across the skin, it can be absorbed into the lungs, across the eyes. It's pretty gruesome stuff," he said on CNN's "Piers Morgan Live." "It is so indiscriminate...So you don't even know that you've been exposed, necessarily, until you suddenly start to get sick. And then, it starts pretty quickly and can degrade pretty quickly as well."
12:27 p.m. ET -- John Kerry: "We're here because a dictator and his family's enterprise...were willing to infect the air of Damascus that killed innocent mothers and fathers and children...during the early morning hours of August 21."
Kerry announced Sunday that blood and hair samples from eastern Damascus, Syria, "tested positive for signatures of sarin" gas. Kerry said on CNN's "State of the Union" that the U.S. obtained the samples independently from "first responders" and through an "appropriate chain of custody"," not from the United Nations chemical weapons inspectors. Read more.
12:21 p.m. ET -- Rep. Eliot Engel, the top Democrat on the committee, gives his opening statement, saying he supports the president's proposal to take action but does not favor giving the president a "blank check." He argues American troops must not be committed to Syria, and the U.S. should redouble its efforts to help the opposition. "If we do not pass the authorization, what message will Assad get?"
Engel appeared on CNN two days ago, explaining the so-called "red line" and the difference between the situations in Syria and Iraq.
12:20 p.m. ET -- Chairman Ed Royce: "Over a year ago, President Obama drew a "red-line" -- yet only last week did the Administration begin to consult with Congress on what that means.
Today, the House begins formal consideration of the President's request to use military force in Syria. It's a cliché, but true: there are no easy answers. Syria and much of the Middle East are a mess. So we look forward to a through and deliberate discussion today, one reflecting the gravity of this issue."
12:19 p.m. ET -- Chairman Ed Royce: "There are concerns. The President promises a military operation in Syria of limited scope and duration. But the Assad regime would have a say in what happens next. That'd be particularly true as President Obama isn't aiming to change the situation on the ground. What are the chances of escalation? Are different scenarios accounted for? If our credibility is on the line now, as is argued, what about if Assad retaliates? Americans are skeptical of getting near a conflict that, as one witness has noted, is fueled by 'historic ethnic, religious and tribal issues.'"