By Khaled Yacoub Oweis
AMMAN, June 14 (Reuters) - Syrian rebels and activists say they fear President Bashar al-Assad's troops could resort to wider use of chemical weapons, unless the United States follows up on its pledge of military support with firm and swift action.
After months of equivocating, President Barack Obama's administration said on Thursday it would arm rebels, having obtained proof the Syrian government used chemical weapons against fighters trying to overthrow President Bashar al-Assad.
Western diplomats said the United States is considering imposing a no-fly zone in Syria, in what would be its first direct military intervention of the two-year-old civil war.
Rebels inside Syria, frustrated by what they see as endless Western delays, said that public statements alone would not deter Assad and his pro-Iranian Hezbollah allies.
They said Assad could shift the use of chemical weapons, so far reportedly deployed mainly to check rebel advances, to a more offensive capability for recapturing territory.
"The U.S. announcement upped the ante but it remains a verbal response that will not change Assad's intentions," said Abu Hamza al-Dirani, a member of the Revolution Command Council in the southwestern Damascus suburb of Daraya, which activists said was hit by a sarin gas attack in April.
"The regime remains undeterred. Assad regards everyone who is not supporting him a terrorist and he will not hesitate to commit another Halabja in Syria," Dirani said.
The Kurdish town Halabja in northern Iraq was target of a chemical weapons attack by Saddam Hussein's forces in 1988 that killed thousands of civilians.
Washington said 100 to 150 people were killed in what it called "detected chemical attacks" in Syria. That is a tiny fraction of the 90,000 death toll from two years of conflict, yet it marks the crossing of a "red line" on the use of chemical weapons, U.S. officials said.
Syrian authorities say the military would not use chemical weapons against its own people and accuse the opposition of using the weapons.
President Barack Obama's deputy national security adviser, Ben Rhodes, mentioned four cases since March - two around the northern city of Aleppo, one north of Homs and one east of Damascus - where chemical agents including sarin were used.
Activists have reported several other cases.
Dirani said the sarin gas attack on Daraya on April 26 wounded dozens of people, but that the proximity of Daraya to a district inhabited by Assad's minority Alawite sect deterred a wider use of the deadly chemical.
The Alawites, an offshoot of Shi'ite Islam, have controlled Syria, which is majority Sunni Muslim, since the 1960s. They dominate the army and security apparatus, especially specialised units such as chemical weapons and missile squadrons.
One opposition activist in Damascus said chemical weapons have been used in around the Harasta highway, which straddles several Damascus neighbourhoods largely held by rebels, such as Jobar, Qaboun and Barzeh, and in the Ghouta, an expanse of Sunni Muslim working class population centres and farmland east of Damascus that have been at the forefront of the revolt.
In the last two months, fighters from the Shi'ite Lebanese guerrilla group Hezbollah have been sent to help secure areas in Ghouta hit by chemical weapons, he said.
"Until now the regime has confined the use of sarin to certain fronts. But it appears intent now on capturing northern and eastern neighbourhoods of Damascus, so we could see the scale of use of chemical weapons changing, and masses of civilians getting killed," the Damascus activist said.
"Assad needs to be hit hard to understand that there are consequences to what he is doing. Otherwise he has the capacity and willingness to use chemical weapons for mass killings."
Rebel commander Abu Ghazi, who operates in the eastern Ghouta, where rebels have been on the defensive in recent weeks, said a U.S. hit was needed to dispel a widening popular conception that the United States was colluding with Assad in the use of chemical weapons.
"The pattern we have been seeing is whenever we advance he uses chemical weapons," Abu Ghazi said. "Most of the Ghouta is now under siege, and Assad is not in a hurry. He is gauging the reaction of the international community every time he uses sarin and if the lame response continues, he will use chemical weapons to try and retake the Ghouta," he added. (Editing by Dominic Evans and Janet McBride)