Haley accused Russian Federation and Iran of having little interest in a political solution and called their actions those of "cowards interested in a bloody military conquest".
It was the second day of bombardment on the jihadist and rebel-held province and adjacent areas, after key powerbrokers in Tehran failed to reach a deal to avert a government assault.
According to US officials, the Russians have twice threatened to conduct military operations in the area over the last 10 days, prompting the USA military to warn against any such move and deploy Marine reinforcements to the area.
The Syrian Observatory for Human Rights said 21 pro-regime fighters had been killed in an Isil ambush on Monday in southern Syria. "I won't give you more details, but this is your warning", the militant said in video footage circulating on social media. The Americans, Russians, Iranians, Turks, Israelis and more have all been involved in Syria's conflict to varying degrees, turning it into a proxy battleground for various global interests.
A possible regime attack on Syria's northwestern province of Idlib will sabotage the ongoing political process and cause a serious crisis of confidence, the Turkish presidential spokesman said on September 11.
Meanwhile, Turkey, which already hosts three million Syrian refugees, is keen to prevent an assault that would see hundreds of thousands more mass along its border.
Idlib and its surrounding area are home to some 3 million people, including more than a million civilians displaced from other parts of Syria.
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Maria Manfredini, a long-term resident in the area, described the incident as "tragic on every level". Assistant Commissioner Steel said there were "no ongoing safety concerns" at the scene.
The intense air raids came a day after Iran and Russian Federation backed a military campaign in the rebel-held area despite Turkey's pleas for a ceasefire.
OCHA spokesman David Swanson told Reuters that as of Sunday, 30,542 people had been displaced from northwest Syria, moving to different areas across Idlib.
A journalist and resident of the area, Arin Sheikmos, said the government security troops went on an arrest campaign in Kurdish-controlled areas, detaining people it accuses of skipping compulsory military service.
"It is a very major preoccupation for us", he said.
The Observatory described the attacks on the rebel-held areas as the "most intense" since August and said they killed four in Abdeen, west of Khan Sheikhoun town, including two children and a woman.
Turkey has renewed calls for worldwide backing for a ceasefire in Idlib, telling the United Nations security council that an all-out assault on Syria's rebel-held province would trigger a huge wave of refugees and could threaten Europe.
"I'm not going to tell the world ahead of time what we're going to do". Civilians and fighters have poured in, shuttled out of towns and cities where Assad's military crushed rebels with the help of Russian Federation and Iran.
Syria's conflict has killed more than 350,000 people and forced millions more out of their homes, but the United Nations has warned a full-blown attack on Idlib could bring unprecedented suffering.