BEIRUT (Reuters) - When Abu Ahmad stepped out of his house in Raqqa after a night of heavy air strikes, he found several of his neighbors lying dead in the street.

FILE PHOTO: A Kurdish fighter from the People's Protection Units (YPG) looks at a smoke after an coalition airstrike in Raqqa, Syria June 16, 2017. REUTERS/Goran Tomasevic/File Photo

“I went out the next morning just to inspect,” he said. “I swear to God, cats were eating the corpses.”

“We couldn’t do anything with the dead bodies,” he told Reuters in a series of voice messages from the city, the global headquarters of Islamic State. “They were just abandoned. We informed the hospital.”

The U.S.-led coalition battling to defeat the ultra-hardline militants in Raqqa says it goes to great lengths to avoid civilian casualties.

Abu Ahmad said air and artillery attacks were relentless, leaving most people holed up inside, unable to bury the dead and paralyzed by fear of the warplanes and shelling by U.S.-backed forces fighting on the ground.

“We don’t dare come out of our houses,” he said. “There is death everywhere, the stench of death, of destruction. It’s terrifying.”

He declined to give his full name out of fear for his life and his account could not be independently verified: Islamic State has imposed tight controls on communications in Raqqa, and routinely executes people accused of spying or treachery.

He said he had encountered few Islamic State militants or armored vehicles recently in his district, which lies close to a front line in the west of the city. Many of those he did see were teenage boys with Kalashnikovs and rocket-propelled grenades.

Under the banner of the Syrian Democratic Forces, Kurdish and Arab militias are now fighting inside the historic Old City, after pushing into Raqqa last month.

SCREAMED FOR HELP

On one particularly bad day last month, Abu Ahmad had just returned from getting water at a nearby well when he said intense air strikes battered his district around Raqqa’s al-Nour mosque.

Jets pounded buildings and cars near the neighborhood bakery, killing more than 30 people, he said. The U.S.-led coalition said it was investigating the allegation.

People screamed for help in the dark and houses crumbled as the bombs fell, Abu Ahmad recalled. “Imagine...we couldn’t even do anything. The rocket launchers, the warplanes. We left them to die under the rubble,” he said.

A few men went out to search for and rescue the injured, but they could not get any of the dead bodies out.

The Kurdish-led SDF has said it is careful to safeguard civilians in Raqqa, which Islamic State has used as a hub to plot attacks abroad.

The U.S.-led coalition also says it takes “all reasonable precautions” to avoid civilian casualties in its bombing runs in Syria and Iraq.

Ahead of the final assault on Raqqa city, the U.N. human rights office raised concerns about increasing reports of civilian deaths in the area. In a May report, it said there had been “massive civilian casualties” already.

The United Nations estimates that 50,000 to 100,000 people are trapped in Raqqa. Witnesses said the militants have shot at those trying to escape, and people who have left in recent months reported paying large sums to smugglers to get them out.

Abu Ahmad said his parents and children had been smuggled out of the city. “We had stocked food a while ago in anticipation of the siege,” he added. “But this fierce attack, we hadn’t expected even one percent of this, we would have left Raqqa immediately (if we’d known).”

The U.S.-led coalition said before the assault on Raqqa that 3,000 to 4,000 IS militants were still there, even after leaders abandoned the city for territory further south.

The SDF says that Islamic State has heavily mined the old quarters of Raqqa and that the militants are doing most of their fighting at night without moving much in the daytime.

Reuters lost contact this week with Abu Ahmad. In his final message, he said he planned to get smuggled out of Raqqa and escape to the countryside.

“That’s it. It’s unbearable,” he said.

“We are living in a horror movie.”