US Vice President JD Vance told reporters on Thursday that the US is "very fully" investigating the military's reported strikes on a wedding in Iran which killed at least four people this week.

There were at least a dozen other victims along the southern coast of Iran after the US unleashed a barrage of attacks in one of the largest flare-ups since the Islamabad Memorandum of Understanding was signed between the two sides more than two months ago.

"I've been briefed to the extent that I know that we're investigating," Vance said during the White House briefing.

"I will say that the Iranian state media has not been a very good scribe about what's happened in the conflict thus far. So I'm extremely sceptical of this," he added.

"The United States never targets civilians in combat. We never will do that. We never have done that. And unfortunately, obviously, sometimes things happen... When our military makes mistakes, they learn from them to try to get better from them. So we're investigating it very fully."