DUP MP Nigel Doods, reacting to the air strikes, said: "First and foremost we salute the courage of our fearless servicemen and women".
In the biggest foreign military action so far against Syria's regime, Western officials said a barrage of cruise and air-to-land missiles hit targets near Damascus and in Homs province including a scientific research centre, storage facilities and a command post.
May said the missile strike, created to minimize civilian casualties, was aimed at deterring further use of chemical weapons and was not an attempt to topple the Syrian government.
"Important infrastructure was destroyed which will result in a setback for the Syrian regime", Mattis said.
May said Britain and the West had an obligation to deter both Assad and others from using chemical weapons after the poison gas attack in Douma near Damascus killed up to 75 people including children.
"It was right to take the action that we have done in the timing that we have done", she said. "Let these united actions send a clear message to the regime - the use of chemical weapons is categorically unacceptable and you will be held to account".
Earlier, the US, Great Britain and France claimed the strikes had been conducted in response to an alleged chemical weapons attack in Douma, a suburb of the Syrian capital. Russian Federation and Syria claim the attack was fabricated. Britain has accused Russia of being behind last month's nerve agent attack on former Russian spy Sergei Skripal and his daughter in Salisbury, southern England, a charge Moscow has rejected.
The DUP has backed Prime Minister Theresa May's decision to authorise air strikes in Syria.
The Russian embassy noted that "the gist of British reasoning is that the whole worldwide community recognizes that a "new" chemical attack in Syria is imminent and that only the air strikes could prevent it".
He also did not rule out future military action.
Meanwhile Labour leader Jeremy Corbyn has said Parliament should have been given a vote ahead of the strikes.
British jets fired missiles at a Syrian military base suspected of holding chemical weapons ingredients on Saturday in Britain's first military action against President Bashar al-Assad's regime.
Shortly after the military strikes were launched, Scotland's first minister Nicola Sturgeon said United Kingdom foreign policy should be set by Parliament and not Donald Trump after the U.S., United Kingdom and France bombed targets in Syria. "The opposition does not operate helicopters or use barrel bombs".