"In a world with many dangers, this menace must be confronted," said Mr. Obama during a conference from the Rose Garden at the White House Saturday.
Making a case for military action in Syria, Mr. Obama urged Congress to pass a resolution authorizing the use of force.
He says the White House has proof that Syrian President Bashar Assad's regime used chemical weapons on over 1,400 people, including more than 400 children.
Mr. Obama calls the Aug. 21 attack an assault on human dignity that endangers our national security and Syria's neighbors. He says the massacre is the worst chemical weapons attack of the 21st century.
"Here's my question for every member of Congress and every member of the global community. What message will we send if a dictator can gas hundreds of children to death in plain sight and pay no price?," said Mr. Obama.
On Sunday, Secretary of State John Kerry said Washington had evidence of sarin gas used by Syria and that the case for a military attack is building.
Sarin attacks the nervous system and is considered a weapon of mass destruction by the U.N. Mr. Obama's administration learned of the sarin use through samples of hair and blood provided by first responders in Damascus.
After reviewing the new evidence, Kerry says he remains confident that Congress will give Obama the OK to attack.
"We know that the regime ordered this attack, we know they prepared for it. We know where the rockets came from. We know where they landed. We know the damage that was done afterwards," said Kerry. "We've seen the horrific scenes all over the social media, and we have evidence of it in other ways and we know that the regime tried to cover up afterwards, so this case is really an overwhelming case."
The comments come just a day after Mr. Obama stepped back from what appeared to be an imminent missile strike and decided too wait for a green light from Congress.
U.S. Rep. Janice Hahn (D-San Pedro) says she wrote to the president, encouraging him to consult with Congress before taking action.
"I'm not really sure what the scope or duration of this military strike would be," said Hahn. "I'm not sure what it is we're trying to accomplish. I don't know if we have an end game in sight and I think a lot of Americans are remembering, you know Iraq and Afghanistan."
Other Democrats including Congressman Charles Rangel and Republican senator Ted Cruz are not yet ready to side with the president but are relieved he's asking Congress to weigh in.
"That was the right thing to do and in making that situation it seems as though he agrees that there is no imminent threat requiring action before Congress can consider the issues," said Cruz. The president says ground forces would not be involved. He's confident U.S. military intervention would deter chemical weapon attacks in the future.
While Congress considers authorizing military force, retired U.S. Marine Corp. Lt. Col. Hal Kempfer says that allows the U.S. more time to observe the Assad regime as it prepares for a possible strike.
"This may cause them to start moving some stuff which may help us in our targeting over a period of time where we can see different targets, new targets, update our information," said Kempfer. Congress convenes on Sept. 9.
Syrian state-run daily calls Obama move a retreat
In the meantime, a Syrian newspaper is calling President Barack Obama's reluctance to attack Bashar Assad's regime "the start of a historic American retreat."
In a front-page editorial Sunday, the Al-Thawra daily says Obama's reluctance to carry out strikes against Syria stems from his "sense of implicit defeat and the disappearance of his allies." It also says the U.S. president worries about limited intervention turning into "an open war has pushed him to seek Congress' consent."
Al-Thawra is a government newspaper and its editorials reflect the thinking of President Bashar Assad's regime.
Congresswoman Janice Hahn speaks about Syrian conflict after briefing
Congresswoman Janice Hahn was one of the lawmakers called to Washington, D.C., for a classified briefing Sunday.
She returned to Los Angeles Sunday night with the decision weighing heavily on her mind.
She spoke at Los Angeles International Airport.
"I think [Assad] should be held accountable for using chemical weapons. Now, is a military strike, is bombing that country the way we hold him accountable or are there other ways? And i would still like to see us pursue other ways," said Hahn.
Hahn says Congress is divided. She says she'd feel better if more of the international community was behind the U.S.
Local Syrian-Americans react to president's announcement
Several protests were scheduled to be held Sunday in downtown Los Angeles Sunday against military action in Syria.
The groups set to take part in the event include Answer. L.A., Arab Americans for Syria and Veterans for Peace.
Officials say a strike would be a "reckless act of aggression."
Opinions on President Barack Obama's strategy appears to be mixed.
"When it comes to humanity, when it comes to children. Any human being especially the leader of the world, Mr. Obama, has to be stronger about his position. Today I felt my president was weak." Said Duna Khedraki.
"The only thing that's going to happen is more destruction, more death. There is no specific target that is going to come out of this that is positive," said Mazen Almoukdad.
Protests against U.S. military strikes were also held in Sacramento, San Diego, and other cities across the United States.
The Associated Press contributed to this report.