By Elizabeth Piper and Laila Bassam
LONDON/DAMASCUS (Reuters) - Western powers have no plans for further missile strikes on Syria but will assess their options if Damascus uses chemical weapons again, Britain's foreign minister said on Sunday as debate raged over the legality and effectiveness of the raids.
U.S., French and British missile attacks struck at the heart of Syria's chemical weapons program on Saturday in retaliation for a suspected poison gas attack a week ago, and the three countries insisted they were not aimed at toppling President Bashar al-Assad or intervening in a seven-year civil war.
The bombings, hailed by U.S. President Donald Trump as a success but denounced by Damascus and its allies as an act of aggression, marked the biggest intervention by Western countries against Assad and his ally Russia, whose foreign minister Sergei Lavrov called them "unacceptable and lawless".
In Damascus, Syria's deputy foreign minister Faisal Mekdad met inspectors from the global chemical weapons watchdog OPCW for about three hours in the presence of Russian officers and a senior Syrian security official.
The inspectors were due to try to visit the site of the suspected gas attack. Moscow condemned the Western states for refusing to wait for their findings before attacking.
As he left the hotel where the meeting took place, Mekdad declined to comment to reporters waiting outside.
British Foreign Secretary (Minister) Boris Johnson defended Prime Minister Theresa May's decision to take part in the attack, saying it was to deter further use of chemical weapons.
"This is not about regime change … This is not about trying to turn the tide of the conflict in Syria," he told the BBC.
"There is no proposal on the table at the moment for further attacks because so far thank heavens the Assad regime have not been so foolish as to launch another chemical weapons attack."
"If and when such a thing were to happen, then clearly with allies we would study what the options were," he said, echoing U.S. ambassador to the United Nations, Nikki Haley, who told an emergency Security Council meeting that Trump told her that if Syria uses poisonous gas again, "The United States is locked and loaded."
Asked if this meant Assad could carry on using barrel bombs and other means in the war provided he did not use chemical weapons, Johnson said that was the "unhappy" consequence.
Assad was determined "to butcher his way" to an overwhelming victory and only the Russians could pressure him to come to the negotiating table in Geneva, Johnson said.
British opposition leader Jeremy Corbyn said that the legal basis used to support the British role was debatable, adding that he would only support action backed by the UN Security Council.
"I say to the foreign secretary, I say to the prime minister, where is the legal basis for this?" Corbyn said in an interview with the BBC.
The Western countries blame Assad's government for a suspected poison gas attack in Douma on April 7 that killed up to 75 people. Russia, whose ties with the West have sunk to levels of the Cold War-era, denies any gas attack in Douma and said Britain staged it to whip up anti-Russian hysteria.
In Damascus, Assad told a group of visiting Russian lawmakers that the Western missile strikes were an act of aggression, Russian news agencies reported.
Syria released video of the wreckage of a bombed-out research lab, but also of Assad arriving at work as usual, with the caption "Morning of resilience" and there were no immediate reports of casualties.
The Russian agencies quoted the lawmakers as saying Assad was in a "good mood", had praised the Soviet-era air defense systems Syria used to repel the Western attacks and had accepted an invitation to visit Russia at an unspecified time.
Russian Foreign Ministry official Vladimir Ermakov struck a apparently conciliatory tone on Sunday, saying Washington would want to maintain a dialogue with Moscow about strategic stability after the raids, Russian media reported.
"In the U.S. administration there are specific people who it is possible to talk with," said Ermakov, head of the ministry's department for non-proliferation and arms control.
President Trump had said "Mission accomplished" on Twitter on Saturday following the strikes, although U.S. Lieutenant General Kenneth McKenzie at the Pentagon acknowledged elements of the program remain and he could not guarantee that Syria would be unable to conduct a chemical attack in the future.
Russian and Iranian military help over the past three years has allowed Assad to crush the rebel threat to topple him.
The United States, Britain and France have all participated in the Syrian conflict for years, arming rebels, bombing Islamic State fighters and deploying troops to fight the militants. But they have refrained from targeting Assad's government, apart from a volley of U.S. missiles last year.
RED LINE BREACHED?
The strikes suggest Trump may have reset America's red line for military intervention in Syria over the use of chemical weapons.
In Washington, a senior administration official said that "while the available information is much greater on the chlorine use, we do have significant information that also points to sarin use" in the attack.
Sarin had previously appeared to be the threshold for intervention. Chlorine, in contrast, has been used more widely in Syria's conflict without past U.S. reprisals, and the chemical is far easier to find and weaponize, experts say.
Washington described the strike targets as a center near Damascus for the research, development, production and testing of chemical and biological weapons; a chemical weapons storage site near the city of Homs; and another site near Homs that stored chemical weapons equipment and housed a command post.
Iranian Supreme Leader Ayatollah Ali Khamenei called the attack a crime and the Western leaders criminals, while U.N. Secretary-General Antonio Guterres urged all Security Council members to use restraint, but said charges of chemical weapons use demand investigation.
Meanwhile, Pope Francis called on world leaders to renew efforts to bring peace to Syria, saying he was deeply troubled by their failure to agree on a joint plan to end the bloodshed.
GRAPHIC - Details of air strikes on Syria (https://tmsnrt.rs/2EKgAMN)
(Reporting by Elizabeth Piper and Tom Perry; Additional reporting by Phil Stewart, Jeff Mason, Steve Holland, Idrees Ali, Yara Bayoumy, Matt Spetalnick and Joel Schectman in Washington; Michelle Nichols in New York; Samia Nakhoul, Tom Perry, Laila Bassam, Ellen Francis and Angus McDowall in Beirut; Kinda Makieh in Barzeh; Michael Holden and Guy Faulconbridge in London; and Jean-Baptiste Vey, Geert de Clercq and Matthias Blamont in Paris; Andrey Ostroukh and Jack Stubbs in Moscow; Alison Bevege in Sydney,; Writing by William Maclean; Editing by Adrian Croft and Alexander Smith)