Mr Johnson said action had to be taken against Syria for the Douma attack during an appearance on The Andrew Marr Show on Sunday.
But Johnson stressed the "overwhelming purpose" of the mission was a response to a series of chemical attacks in recent years.
The United Kingdom is now not considering further attacks on Syria linked to Damascus' alleged use of chemical weapons, UK Foreign Secretary Boris Johnson said Sunday. Unfortunately, they will not allow you to remove President Bashar al-Assad.
"Entirely the right thing to do".
"I'm afraid the Syrian war will go on in its terrible, miserable way".
Britain and France on Saturday joined the US-led missile strikes, which came a week after a deadly attack on the town of Douma where civilians were hit with chlorine and sarin according to the Western powers.
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They clinched the silverware 24 hours later thanks to Albion forward Jay Rodriguez's 73rd minute header at Old Trafford . United suffered a 1-0 defeat to West Brom on Sunday evening - a result which handed City the Premier League title.
On the same show, Jeremy Corbyn expressed his unease over the strikes and criticised the prime minister for not recalling Parliament to vote on the issue.
The air strikes, carried out by the US, UK and French military, targeted three separate targets in Syria linked to the Assad regime's chemical weapons program.
He also did not rule out further attacks against Syria if the Assad regime continued the alleged use of chemical weapons.
Despite describing the intervention as "successful", Britain's foreign minister said there were now no plans for further attacks.
Mr Johnson said yesterday that the Government is taking "every possible precaution" in preparation for any Russian retaliation in the form of cyber attacks.