Tehran-linked groups targeted US forces in Syria for a second day in a row Friday, after the United States conducted an air strike against their bases following a drone strike Thursday.

White House National Security Council spokesman John Kirby said no American personnel were hurt in the new attack in northeast Syria, calling the incident an initial reaction to US retaliatory strikes on Iran-aligned groups in the area.

"It is not uncommon, when we take a retaliatory strike like this, for them to answer right back with some ineffective rocket fire. And these were largely, completely ineffective," Kirby told MSNBC. "Nobody was hurt, no US casualties at all."

The attack on Thursday with a suicide drone killed a US contractor and injured several servicemen. The US immediately retaliated with air strikes.

The US intelligence community assessed that the one-way attack drone was Iranian in origin, the Pentagon said, a conclusion that could further aggravate already strained relations between Washington and Tehran.

The new rocket attack by Iran-linked forces targeted a US base near the Al-Omar oil field. Lebanese pro-Iranian TV channel Al Mayadeen was first to report the attack.

The attacks by Iranian-led groups come just two weeks after Tehran signed a deal with Saudi Arabia to restore relations, a move seen by analysts as potentially beneficial for stability in the region.