International investigators on Tuesday entered a Syrian town hit by an alleged chemical attack, after days of delay and warnings by Western powers that crucial evidence had likely been removed.

The suspected gas attack on April 7 on Douma, near Damascus, reportedly left more than 40 people dead and was blamed by Western powers on the regime of Syrian President Bashar al-Assad.

In response, the United States, France and Britain conducted unprecedented missile strikes on Syrian military installations, but Paris admitted on Tuesday they were a matter of "honour" that had solved nothing.

"Experts from the chemical weapons committee enter the town of Douma," state news agency SANA wrote, referring to the Organisation for the Prohibition of Chemical Weapons (OPCW).

The inspectors arrived in Damascus on the day of the Western strikes but had not been allowed to enter Douma.

France and the United States appeared to question the purpose of such a mission, warning that any incriminating evidence had likely been removed by now.

"It is highly likely that evidence and essential elements disappear from the site, which is completely controlled by the Russian and Syrian armies," the French foreign ministry said.

The US ambassador to the OPCW, Ken Ward, had claimed Monday that the site and "may have tampered with it".

Russian foreign ministry spokeswoman Maria Zakharova hit back at France, calling the accusation "very surprising" and saying that Russia had supported the inspection.

Several experts have also said however that any investigation at this stage was likely to be inconclusive.

"As with any crime scene, it is crucial to get there as soon as possible," said Olivier Lepick, a fellow at the Paris-based Foundation for Scientific Research.

"If the Russians and Syrians have nothing to hide, it's strange that they would wait 36 to 72 hours," he said. "It's probably to give themselves the time to finish cleaning up."

In an impassioned defence to the European Parliament on Tuesday, France's President Emmanuel Macron admitted that Saturday's strikes had been a more political than military decision.

"Three countries have intervened, and let me be quite frank, quite honest -- this is for the honour of the international community," he said in the French city of Strasbourg.

"These strikes don't necessarily resolve anything but I think they were important," Macron added.

The French leader was also set to strip Syrian President Bashar al-Assad of a prestigious award he was granted by former president Jacques Chirac in 2001.

"The Elysee confirms that a disciplinary procedure for withdrawing the Legion d'Honneur (Legion of Honour) is under way," Macron's office said.

The war of words continued to spiral between the Russian-backed Syria regime and the West but a military escalation looked to have been averted despite both sides trading threats after the strikes.

Yet, a report on SANA that Syrian air defences had shot down missiles over Homs province overnight raised fears that further action had indeed been taken.

It branded the incident an "aggression" but did not name a specific country.

Explosions were heard near Shayrat air base, southeast of Homs city, and near Damascus where two other air bases are located, the Syrian Observatory for Human Rights reported.

Later Tuesday, however, SANA retracted the report, stressing there had been "no external attack" on Syria.

"Last night, a false alarm that Syrian air space had been penetrated triggered the blowing of air defence sirens and the firing of several missiles," a military source told the agency.

After Saturday's strikes, which destroyed mostly empty buildings, the trio of Western powers trying to reassert influence on the seven-year-old war have appeared to favour diplomatic action.

A series of meetings was scheduled in a bid to relaunch talks aimed at ending a war that has left more than 350,000 people dead and displaced more than half of the Syrian population.

Analysts have said however that it would take more for the West to mount a meaningful challenge to Russia's weight as a broker.

"For a new diplomatic initiative to work, the balance on the ground must be changed," said Nabeel Khoury.

"As it is, even with this latest bombing, the West does not have a seat at the table," said the former US diplomat, currently a fellow at the Atlantic Council think-tank.

Macron has said he saw last week's strikes as a way of engineering a split in the alliance formed by Damascus, Moscow, Tehran and Ankara in the conflict.

Russia appeared in no mood to extend a hand to the West on the Syria file however and its ambassador to the UN, Vassily Nebenzia, called the diplomatic push "untimely".

And a Turkish presidential source said after telephone talks between Turkish President Recep Tayyip Erdogan and Iranian counterpart Hassan Rouhani that the two sides had vowed the alliance must continue.