The US carried out major airstrikes against the Islamic State (IS) in Syria on Friday, fulfiling President Donald Trump’s vow to avenge the deaths of two US Army soldiers and a civilian US interpreter killed in a terrorist attack in the central part of the country last Saturday.

American fighter jets, attack helicopters and artillery fired more than 100 munitions at more than 70 suspected Islamic State targets at several locations across central Syria, including weapons storage areas and other buildings to support operations, the military’s Central Command said in a statement. It said Jordanian warplanes assisted in the operation.

The American air and artillery attacks were expected to last several hours, deep into early Saturday morning in Syria, in what Trump described as "a massive strike".

Social media accounts in Syria reported explosions across wide swaths of the country.

Defence secretary Pete Hegseth sought to tamp down fears that the US might reopen a major new war in West Asia, but also suggested that increased attacks against the Islamic State would continue.

“This is not the beginning of a war — it is a declaration of vengeance,” Hegseth said on social media. “The United States of America, under President Trump’s leadership, will never hesitate and never relent to defend our people.”

Hegseth added: “Today, we hunted and we killed our enemies. Lots of them. And we will continue.” He offered no other details about the strikes.

In a rally-style speech on Friday night in North Carolina, Trump called the attacks "very successful".

“We hit the ISIS thugs in Syria who were trying to regroup after their decimation by the Trump administration five years ago,” he said. “We hit them hard.”

The soldiers slain last Saturday were the first American casualties in the country since the fall of the dictator Bashar al-Assad last year. They were supporting counterterrorism operations against the Islamic State in Palmyra, a city in central Syria, when they came under fire from a lone gunman, American and Syrian officials said.

No group has claimed responsibility for the attack, though initial assessments suggest that it was most likely carried out by the Islamic State, according to the Pentagon and American intelligence officials.

New York Times News Service