The US has expressed serious concerns the Syrian regime led by its embattled leader, President Bashar al-Assad, could have come up with a new type of sophisticated chemical weapon to tackle its opponents in the long-running civil war.

President Donald Trump administration in the White House believes it is possible that Assad's forces may be developing this chemical weapon either in its attempt to improvise the capabilities or to escape a possible detection. Reports have also emerged the forces loyal to the Syrian president have already used such deadly weapons in Eastern Ghouta on Thursday (1 February).

"Russia is making the wrong choice by not exercising its unique influence. To allow [the] Syria regime to use chemical weapons against its own people is unconscionable. We will pursue accountability," said the US State Department spokesperson Heather Nauert. The department was echoing comments made by the US Secretary of State Rex Tillerson, who said Moscow, a key Syrian ally, should also be held partially accountable for failing to enforce a strict ban on the use of chemical weapons.

American officials have told multiple US media outlets that Assad's regime has kept chemical weapons, officially banned by UN regulations, hidden inside the war-torn country despite an agreement to abolish those in 2013.

Those unnamed officials from the Trump administration have said, according to Reuters, Washington has not ruled out the possibility of a military action in order to deter Damascus from employing chemical weapons. The Islamic State (Isis) group has been accused of using mustard and chlorine gas in the civil war by delivering those using shells or improvised explosive devices.

These charges surface just as when the Syrian regime is thought to be behind a suspected chlorine attack on Eastern Ghouta, one of the last strongholds held by anti-Assad rebels, recently. In a site located on the outskirts of capital Damascus, at least three civilians were killed and many others left injured, according to the White Helmets.

"3 civilians killed and many injured, including suffocation cases among children, women and #CivilDefense volunteers! 28 air raids, 70 surface-to-surface missiles, some loaded w/chlorine gas and 200 artillery shells targeted cities in #Eastern_Ghouta today!#Doumasuffocating",

UN expert Ghouta sarin attack
A United Nations (UN) arms expert collects samples on August 29, 2013, as they inspect the site where rockets had fallen in Damascus' eastern Ghouta suburb during an investigation into a suspected chemical weapons strike near the capital Ammar al-Arbini/AFP/Getty Images