Here is a look at some of the main military assets that could be involved in an offensive.

- United States -

When President Donald Trump last year ordered a strike against Assad following a deadly sarin gas attack on the rebel-held town of Khan Sheikhun, the US Navy launched 59 Tomahawk cruise missiles from the destroyers USS Porter and USS Ross in the eastern Mediterranean.

This year, the Porter and the Ross are both conducting operations in the Northern Atlantic, well out of range of a Syria strike.

But the USS Donald Cook, an Arleigh Burke-class guided-missile destroyer, left port at Larnaca, Cyprus on Monday and is within easy striking range of Syria.

Additionally, the USS New York is underway in the Mediterranean, though the amphibious transport ship is unlikely to be directly involved in a strike.

The Navy also has eight submarines currently deployed globally.

Their location is a tightly held secret, but if one is in the Mediterranean it could be used in a cruise missile strike.

The Tomahawks used last year targeted aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defense systems and radars at the Shayrat air base.

Currently, the US Navy has no aircraft carriers in the Med, though the USS Harry S. Truman Carrier Strike Group is due to leave Norfolk, Virginia on Wednesday as part of a regular deployment with the Navy's Sixth Fleet, which is headquartered in Naples, Italy.

In the event the Pentagon decides to use manned warplanes or drones, the US military has an intricate infrastructure in place in the region, where it has led an air war against the Islamic State group in Syria and Iraq since 2014.

- France -

If France joins a strike, it could launch its Rafale warplanes from French soil and use aerial refueling to get them to the target region.

This was the preferred course of action chosen by France's then president Francois Hollande in August 2013, after chemical attacks in Ghouta left more than 1,400 people dead.

But ultimately, Barack Obama famously declined to launch an operation in Syria, forcing Paris to stand down even though it had a half dozen Rafales ready at the Saint-Dizier air base in eastern France.

Another possibility is launching strikes from a multi-mission frigate equipped with cruise missiles. A French military official said France permanently has such a ship in the eastern Mediterranean.

- Britain -

Like France and the United States, Britain has established a heavy military presence in the Syrian region as it has supported the fight against IS.

As of 13 February 2018, Britain had conducted 1,700 airstrikes against IS targets in Iraq and Syria.

Royal Air Force Akrotiri is a big base on Cyprus from where Britain launches many of its anti-IS raids in Syria.