U.S. Ambassador to the U.N. Nikki Haley said on Saturday that the U.S. will strike Syria again if the Assad regime uses chemical weapons once more.

"If the Syrian regime uses this poison gas again, the United States is locked and loaded," Haley said, speaking at the U.N. Security Council meeting opened at Russia's request to discuss military strikes carried out by the United States, France and Britain on Syria in response to a suspected chemical weapons attack.

In the opening speech, U.N. Secretary-General Antonio Guterres urged all states on Saturday "to show restraint in these dangerous circumstances and to avoid any acts that could escalate matters and worsen the suffering of the Syrian people."

He said international investigators were in Syria and ready to visit the site of a suspected deadly chemical weapons attack in Douma, which prompted military action by the United States, France and Britain.

Russian Ambassador to the U.N. Vassily Nebenzia said the U.S. and allies have demonstrated a blatant disregard for international law.

Nikki Haley, on the other side, said that the strikes were carefully planned to minimize civilian casualties, adding that the response was justified, legitimate and proportionate.

The U.N. ambassador said the the United States would continue to seek out and call out anyone who uses or aids the use of chemical weapons.

"We are confident that we have crippled Syria's chemical weapons program. We are prepared to sustain this pressure, if the Syrian regime is foolish enough to test our will," she said.

"Russia is calling an emergency session of the UN Security Council to discuss the aggressive actions of the US and its allies," the Kremlin said in an earlier statement.

The statement also condemned the air strikes on Syria where its armed forces are backing regime leader Bashar al-Assad.

"Russia severely condemns the attack on Syria where Russian military are helping the lawful government in the fight with terrorism," the Kremlin in its first reaction to the strikes.

Russia said that the Western powers "cynically" carried out military action hours before a team from the Organisation for the Prohibition of Chemical Weapons was set to begin an investigation into the suspected chemical weapons attack in the town of Douma in Eastern Ghouta that sparked the intervention by the US and its allies.

The current escalation of the situation in Syria "has a destructive effect on the whole system of international relations," the Kremlin said.