(WASHINGTON) -- Secretary of State John Kerry indicated Monday that the Obama administration intends to hold the Syrian regime accountable for a chemical attack that he called "undeniable."
Kerry spoke as the Obama administration was mulling possible military action following reports of a massive chemical weapons attack, with many of the victims being civilians.
And his comments came hours after U.N. inspectors were fired upon by at least one sniper as they tried to enter the area to carry out an investigation to probe the claims of the chemical attack.
Kerry said that the attack was "inexcusable and undeniable," and that the judgment on who is responsible is "very clear to the world."
"We know that the Syrian regime maintains custody of these chemical weapons. We know that the Syrian regime has the capacity to do this with rockets. We know that the regime has been determined to clear the opposition from those very places where the attacks took place," he said.
The regime of Syrian President Bashar al-Assad had denied using chemical weapons and blamed the attack on the rebels his soldiers are battling.
But the secretary of state pointed to the regime's behavior in the wake of the attack as further evidence of guilt.
"For five days the Syrian regime refused to allow the U.N. investigators access to the site of the attack that would allegedly exonerate them. Instead, it attacked the area further, shelling it and systematically destroying evidence. That is not the behavior of a government that has nothing to hide. That is not the action of a regime eager to prove to the world that it had not used chemical weapons. In fact, the regime's belated decision to allow access is too late and is too late to be credible," Kerry said.
For all the outrage, Kerry did not speak of any specific consequences or actions the U.S. planned to take. He said President Obama continues to consult with Congress and U.S. allies and will soon make a decision.
"Make no mistake: President Obama believes there must be accountability for those who would use the world's most heinous weapons against the world's most vulnerable people," Kerry said.
A senior State Department official said that a formal assessment is likely to come soon, possibly sometime this week.
A U.N. team began its investigation Monday after nearly a week's delay by the Assad government, but the team's car immediately came under fire by at least one sniper, U.N. Secretary-General Ban Ki-Moon said.
"Despite such very difficult circumstances, our team returned to Damascus and replaced their car and proceeded to a suburb of Damascus to carry on their investigation," Ki-Moon told reporters. "They visited two hospitals, they interviewed witnesses, survivors and doctors, they also collected some samples. They are now returning to Damascus."
The secretary-general said that the U.N. will be registering a "strong complaint" to both the Syrian government and opposition rebel leaders about the attack in an effort to prevent more incidents from occurring during the rest of the investigation. The U.N. Security Council is holding an emergency meeting to discuss the current situation in Syria.
Over the weekend the Obama administration deliberated over what action the U.S. should take after finding "very little doubt" that the Syrian government used chemical weapons against its own people.
The president and his national security team met to outline military options that include positioning destroyers currently in the Mediterranean that could be used to carry out limited cruise missile strikes. The purpose of launching the strikes would be to "defer or prevent" another chemical attack by the Assad regime, senior administration officials tell ABC News.
On the diplomatic front, Kerry has been furiously burning up the phone lines to allies and foes, including speaking with Russia's Foreign Minister Sergey Lavrov and Syrian Foreign Minister Moulliam. The call to Moulliam on Saturday was the first time the secretary has spoken to anyone in the Syrian government since taking his post early last year.
A senior State Department official said Kerry made clear that based on information U.S. allies have shared along with other intelligence and analysis "there is very little doubt that a chemical weapon was used by the Syrian regime against civilians in this incident."
He also issued a direct message to Moulliam saying that if, as the Syrian regime claims, it has nothing to hide, it should have allowed immediate and unimpeded access to the site rather than continuing to attack the affected area to block access and destroy evidence.
Assad denied the allegations to the Russian newspaper Izvestia, warning that any military intervention by the U.S. would end in "failure." Assad called the claims that his forces were behind the alleged chemical attack as "an insult to common sense." He said Western leaders should "stop meddling in the affairs of other countries," adding, "If someone dreams of turning Syria into a puppet of the West they won't succeed."
Russia's Lavrov has been on his own diplomatic push, speaking with European officials and warning that Russia sees the talk of military strikes as being similar to the drumbeat of war leading up to the invasion of Iraq.
At a press conference in Moscow on Monday, he blasted the United States and its Western allies for making decisions based on growing "hysteria" over last week's attack and accused the West of jumping to conclusions about who was responsible before the U.N. team has submitted its report.
"The region is destabilized in an unprecedented way. So everyone should be responsible," he said, adding that he asked Kerry on the phone Sunday how the U.S. planned to prevent things from leading to regional chaos.
Lavrov repeated several times that an intervention in Syria would have the same destabilizing influence as Iraq and Libya, drawing the entire region into the conflict.
Russia also has doubts about the reliability of the evidence that the Assad regime has used chemical weapons, he said, despite Internet experts noting that the YouTube videos released so far match the timeline of the accusations. Lavrov warned that talk of military options is getting in the way of diplomatic efforts by the U.S. and Russia to hold an international conference to find a diplomatic solution, something the Obama administration has repeatedly said it is committed to.
The foreign minister implied that the driving force behind any military action on Syria was not human rights concerns, but a Western obsession with interfering on their "short electoral cycles" and the "need to satisfy voters."
Copyright 2013 ABC News Radio