BAGHDAD — The American-led military coalition in Iraq said Friday that it was investigating reports that scores of civilians — perhaps as many as 200, residents said — had been killed in recent American airstrikes in Mosul, the northern Iraqi city at the center of an offensive to drive out the Islamic State.
If confirmed, the series of airstrikes would rank among the highest civilian death tolls in an American air mission since the United States went to war in Iraq in 2003. And the reports of civilian deaths in Mosul came immediately after two recent incidents in Syria, where the coalition is also battling the Islamic State from the air, in which activists and local residents said dozens of civilians had been killed.
Taken together, the surge of reported civilian deaths raised questions about whether once-strict rules of engagement meant to minimize civilian casualties were being relaxed under the Trump administration, which has vowed to fight the Islamic State more aggressively.
American military officials insisted on Friday that the rules of engagement had not changed. They acknowledged, however, that American airstrikes in Syria and Iraq had been heavier in an effort to press the Islamic State on multiple fronts.
Col. John J. Thomas, a spokesman for the United States Central Command, said that the military was seeking to determine whether the explosion in Mosul might have been prompted by an American or coalition airstrike, or was a bomb or booby trap placed by the Islamic State.
“It’s a complicated question, and we’ve literally had people working nonstop throughout the night to understand it,” Colonel Thomas said in an interview. He said the explosion and the reasons behind it had “gotten attention at the highest level.”
As to who was responsible, he said, “at the moment, the answer is: We don’t know.”
Iraqi officers, though, say they know exactly what happened: Maj. Gen. Maan al-Saadi, a commander of the Iraqi special forces, said that the civilian deaths were a result of a coalition airstrike that his men had called in, to take out snipers on the roofs of three houses in a neighborhood called Mosul Jidideh. General Saadi said the special forces were unaware that the houses’ basements were filled with civilians.
“After the bombing we were surprised by the civilian victims,” the general said, “and I think it was a trap by ISIS to stop the bombing operations and turn public opinion against us.”
General Saadi said he had demanded that the coalition pause its air campaign to assess what happened and to take stricter measures to prevent more civilian victims. Another Iraqi special forces officer, who spoke on the condition of anonymity because of the sensitivity of the subject, said that there had been a noticeable relaxing of the coalition’s rules of engagement since President Trump took office.
Before, Iraqi officers were highly critical of the Obama administration’s rules, saying that many requests for airstrikes were denied because of the risk that civilians would be hurt. Now, the officer said, it has become much easier to call in airstrikes.
Some American military officials had also chafed at what they viewed as long and onerous White House procedures for approving strikes under the Obama administration. Mr. Trump has indicated that he is more inclined to delegate authority for launching strikes to the Pentagon and commanders in the field.
This is the second time this week that the military has opened an investigation into civilian deaths reported to have been caused by American airstrikes. On Tuesday, Central Command said it was investigating an American airstrike in Syria on March 16 that officials said killed dozens of Qaeda operatives at a meeting place that activists and local residents maintain was part of a religious complex.
While Defense Department officials acknowledged that the building was near a mosque, they called it an “Al Qaeda meeting site” in Jina, in Aleppo Province.
Pentagon officials said that intelligence had indicated that Al Qaeda used the partly constructed community meeting hall as a gathering place and as a place to educate and indoctrinate fighters.
But the Syrian Observatory for Human Rights said that 49 people had been killed in what the group described as a massacre of civilians who were undergoing religious instruction in an assembly hall and dining area for worshipers. The group has produced photos taken at the site after the strike that show a black sign outside a still-standing adjoining structure that identified it as part of the Omar ibn al-Khatab mosque.
Chris Woods, director of Airwars, a nonprofit group that monitors civilian deaths from coalition airstrikes in Syria and Iraq, said that in March alone the number of reported civilian fatalities has shot up to 1,058, from 465 in December, the last full month of the Obama administration.
“We don’t know whether that’s a reflection of the increased tempo of the campaign or whether it reflects changes in the rules of engagement,” he said. But, he added, the recent spike in numbers “does suggest something has shifted.”
American military officials said that what has shifted is that the Iraqi military, backed by the American-led coalition, is in the middle of its biggest fight so far — the battle to retake Mosul from the Islamic State, also known as ISIS or ISIL.
In particular, the campaign for West Mosul has involved block-by-block fighting in an urban environment.
“There’s been no loosening of the rules of engagement,” said Capt. Jeff Davis, a Pentagon spokesman. “There are three major offensives going on right now, at the same time,” he said, citing the battle for West Mosul; the encirclement of Raqqa, Syria, the Islamic State’s de facto capital; and the fight for the Tabqa Dam in Syria.
“There are other people on the battlefield, too,” he said. “It’s close quarters.”
American officials said that even the timing of the strike was still in question. Col. Joseph E. Scrocca, a spokesman for the American-led command in Baghdad, said in a statement Friday that the strike under investigation happened between March 17 and Thursday.
The civilian death toll in Mosul was already widely described as heavy on account of Islamic State snipers and bombs, and intensified urban fighting in which artillery has been used. But there have been numerous reports from witnesses, including rescue workers and residents fleeing the fighting, about bodies being buried under rubble after heavy air bombardment.
Many of the reports centered on the Mosul Jidideh neighborhood, where residents said airstrikes hit a number of houses in recent days, killing dozens, including many children.
Capt. Ahmed Nuri, a soldier with Iraq’s elite counterterrorism forces, who work closely with the American military and call in airstrikes, said on Thursday that his men, facing heavy sniper fire, helped collect five bodies from the rubble of a destroyed home. He said four of them were brothers — named Ali, Omar, Khalid and Saad — whose bodies were delivered to their grieving mother.
The mother, Captain Nuri said, identified the fifth dead body as that of an Islamic State sniper who had been firing at advancing Iraqi forces from the roof of their house.
Local officials have reacted with outrage at the latest civilian deaths, warning that they will make it more difficult to fully take the city, and will alienate civilians still in Mosul, whom the Iraqi government is counting on for assistance.
“The repeated mistakes will make the mission to liberate Mosul from Daesh harder, and will push civilians still living under Daesh to be uncooperative with the security forces,” said Abdulsattar Alhabu, the mayor of Mosul, using the Arabic acronym for the Islamic State.
Mr. Alhabu estimated that at least 200 civilians had been killed in airstrikes in recent days in Mosul.