The heads of U.N. organizations responsible for food assistance and well being of refugees visited Damascus, the Syrian capital, as a growing number of people traveled to the Kurdistan region of Iraq, the U.N. refugee agency UNHCR said.
The officials said Iraq already faces "major security challenges" because it has 1.1 million internally displaced citizens and has now taken in 200,000 Syrians on top of that.
"With the escalation of this conflict, Syria could be on the edge of an abyss," UNHCR chief Antonio Guterres said in a statement. "This war has resulted in a humanitarian calamity without parallel in recent history."
Guterres said "there can be nothing more important" to the Syrian people during the conflict that to keep borders open.
World Food Program Executive Director Ertharin Cousin called on the global community to "come together to ensure the violence ends and the healing begins. The children of Syria are depending on us not just to meet their needs today but to provide hope for a better tomorrow."
Hagel said the Department of Defense has provided the president with "all options for all contingencies."
"He has seen them, we are prepared," Hagel said. "We are ready to go."
Hagel said U.N. inspectors have been collecting intelligence in Syria that makes it "pretty clear" the Syrian government used chemical weapons.
"I think the intelligence will conclude that it wasn't the rebels who used it, and there'll probably be pretty good intelligence to show is that the Syria government was responsible," he said. "But we'll wait and determine what the facts and the intelligence bear out."
Secretary of State John Kerry said Monday Syrian government shelling had destroyed evidence the government used chemical weapons near Damascus.
The White House said Obama and Canadian Prime Minister Stephen Harper spoke by phone Tuesday "to discuss their grave concern" about Syria's reported use of chemical weapons.
"The United States and Canada strongly oppose the use of chemical weapons, and the president and prime minister pledged to continue to consult closely on potential responses by the international community," the White House said in a statement.
British Prime Minister David Cameron said Tuesday lawmakers have been asked to return to London to vote Thursday on a response to the use of chemical weapons.
Cameron's office said Britain's military was making "contingency plans" concerning Syria, CNN reported.
Italy won't participate in any military action against Syria without a U.N. Security Council mandate, Foreign Minister Emma Bonino told a parliamentary foreign affairs commission Tuesday.
Bonino told Radio Radicale Monday Italy should "try to avoid turning an international drama into a global one."
"Even a limited intervention runs the risk of becoming unlimited. We must think it over a thousand times, because the repercussions could be dramatic," she said.
Kerry said Monday the Obama administration was weighing options for a response to what Kerry called "undeniable" evidence troops loyal to President Bashar Assad used chemical weapons last week on Syrian civilians.
He called the use of chemical weapons a "moral obscenity" that demanded accountability. Kerry said information would be released soon that backs up claims of the Assad regime's involvement.
In Russia, the Foreign Ministry Tuesday accused the United States of trying to "create artificial groundless excuses for military intervention" in Syria.
Russian Foreign Minister Sergey Lavrov has said there is no proof the Syrian government was involved in last week's reported attack in Damascus suburbs. His ministry -- as well as China's state-run news agency Xinhua -- has compared the Western allegations against Syria to U.S. claims Iraq was hoarding weapons of mass destruction before the U.S.-led invasion in 2003.
The accusations fell apart when no WMDs were found.
U.N. inspectors were expected to begin a second day of investigations Tuesday at sites of reported chemical weapons attacks around Damascus. But Syrian Foreign Minister Walid Moallem said Tuesday's planned trip was delayed until Wednesday because of security concerns, CNN said.
U.N. experts visited Moadamiyet al-Sham Monday, but before they were able to carry out an inspection, snipers fired multiple times at one vehicle, and there was an explosion near the inspection site, the United Nations said. No injuries were reported.
Moallem denied the government was delaying the inspections, blaming rebels instead. He also denied accusations Syria's army removed evidence of chemical weapons from the scene of last week's attack, saying the area was held by rebel forces, labeled "terrorists" by Syrian government leaders.
Government and opposition forces accused each other of using poison gas last week in a number of Damascus suburbs. Syria's opposition said as many as 1,300 people were killed.
During a news conference Tuesday, Moallem said finding the truth about use of chemical weapons is in the Syrian government's interest, al-Alam reported.
Middle East analyst Richard Haass told CNN Kerry's comments "went far out on a limb" and indicated a U.S. strike on Syria was in the works no matter what the U.N. Security Council does. Haass, president of the Council on Foreign Relations, said military action was needed "to underscore the principle, the norm, the taboo that these weapons ought to have."
Obama likely would order a limited airstrike on Syria to punish it for using nerve gas but won't seek to topple the Assad regime, U.S. officials told The Washington Post.
The strike, whose timing was left open but described as all but inevitable, would likely be conducted with U.S. allies and would probably last only a day or two, officials said.
It would probably involve long-range guided cruise missiles launched from sea or from bombers, the officials said.
Missile-armed U.S. warships are positioned in the Mediterranean Sea. A British nuclear-powered submarine is in the Mediterranean and several British warships are on their way.
British military aircraft are building up at a large Royal Air Force base on Cyprus, British newspaper The Guardian reported.
The United States postponed a meeting with Russia on Syria as U.S. officials mulled the response.
A source at the State Department told CBS News the meeting was scheduled for Wednesday at The Hague, Netherlands, between Undersecretary of State for Political Affairs Wendy Sherman and U.S. Ambassador to Syria Robert Ford, and a delegation of their Russian counterparts.
The agenda was to have included consideration of an international peace conference aimed at ending Syria's civil war, which started in March 2011 when protesters began demonstrating peacefully against Assad's rule.