There is a "high probability" that Syria deployed chemical weapons in the ongoing civil war, but final verification is needed, the chairman of the U.S. House Intelligence Committee told CNN on Tuesday.

"I have a high probability to believe that chemical weapons were used," Chairman Mike Rogers (R-Michigan) told CNN's Wolf Blitzer. "We need that final verification, but given everything we know over the last year and a half, I would come to the conclusion that they are either positioned for use, and ready to do that, or in fact have been used."

Rogers and Sen. Dianne Feinstein (D-California), chairwoman of the Senate Intelligence Committee, struck ominous tones in an interview on CNN's "The Situation Room" about the possibility that Syria had crossed what President Barack Obama has said was a "red line" that could lead to the United States getting involved militarily in the conflict.

Rogers' statement comes as the specter of chemical weapons attacks in the Syrian civil war emerged Tuesday, with the government and rebels each blaming the other for using such munitions.

In remarks earlier Tuesday, White House Chief of Staff Denis McDonough told Jake Tapper on CNN's "The Lead" that the president takes the issue of chemical weapons in Syria "very, very seriously."

If reports of chemical warfare are substantiated, McDonough told CNN, "this is a game changer, and we'll act accordingly."

Intelligence Committee members received the same briefing given to the White House, Feinstein said.

"The White House has to make some decision in this. I think the days are becoming more desperate. The regime is more desperate," Feinstein said in the interview. "We know where the chemical weapons are. It's not a secret that they are there, and I think the probabilities are very high that we're going into some very dark times."

Feinstein and Rogers stressed that a final verification is needed.

CNN national security contributor and former homeland security adviser Fran Townsend said the United States should be able to get verification in "pretty short order."

If the U.S. and its allies decide to act militarily, ground troops will be needed to secure known sites, she said.

The embattled government of President Bashar al-Assad accused rebels of a deadly chemical weapons missile attack

At least 25 people died and more than 110 others were injured Tuesday in the town of Khan al-Asal in Aleppo province, Syrian state media said, quoting government figures. Rebels rebuffed the claims and blamed the government.

The town of Ateibeh, in eastern Damascus, endured "fierce shelling with chemical rockets," an opposition group said. An unknown number of casualties were reported.

These claims come amid pressure in the West to arm rebels, long overmatched by the Syrian military and its allies. The United States and other world powers have worried that Syria would consider using its chemical weaponry arsenal against fighters trying to topple the al-Assad government. And there is concern that jihadists who are fighting on the side of the opposition could get their hands on chemical weaponry.

The civil war -- which began two years ago after a government crackdown on Syrian protesters -- has left around 70,000 people dead, the United Nations said, and uprooted more than 1 million people.

Syrian Information Minister Omran al-Zoubi said the missile in Aleppo province was launched from inside Syria, but the launcher came from another country.

"Whoever paid for this weapon in Qatar or any other country and whoever brought this weapon to be used in Syria must be held accountable, whoever they are, a king or a prince, a president or a minister," he said. "Whoever made this decision in the last Arab League meeting is responsible for the mass killing and the use of weapons of destruction."

Jamal al Ward, head of the military office of the Syrian Coalition, said the opposition has "no chemical substances and no mechanism for producing" such weapons.

"The regime has these weapons and everyone knows where they keep them. They have missiles and factories where they make missiles with chemicals. They are the ones capable of using this stuff all over Syria," he said.