Underlining an open support for US strikes, Johnson claimed it helped "create an opportunity to break the deadlock" and pave the way for a political settlement and a truce, following a succession of failed cease-fires.
British Foreign Secretary Boris Johnson says London will most probably support Washington in the event of further missile strikes on Syria.
Earlier this month the United States fired 59 Tomahawk missiles at a Syrian airbase which was suspected of launching a chemical attack and they have threatened further action.
In an address to British MPs on Tuesday, Johnson said the UK government has not taken any decision yet but would find it "very difficult" to reject a request from the United States regarding attacks on Syria.
The US airstrike this month was the first direct military action taken against President Assad by the US.
Former foreign minister Alistair Burt asked Johnson whether the government felt bound by a previous vote in 2013.
Johnson reiterated that in attacking Syria "the United States has acted with the full support of the British Government", adding that the "only one conclusion" that could be reached based on the known evidence of the alleged chemical attack in rebel-held Idlib province is that "the Assad regime nearly certainly gassed its own people". At the time, the rebels accused the Syrian government of perpetrating a sarin gas attack in a Damascus suburb.
The UK has yet to follow the Donald into Syria, but has backed his actions in launching attacks on "monster" Assad.