The US beat Iran 3-1 (25-16, 25-16, 20-25, 25-20) in Pool B match of the 2015 FIVB World League on Monday.
"USA played better than us again. It’s so difficult to say something," Kovac said in the post match news conference.
"We made so many mistakes. No good face on the court. I’ve stayed with Iran more than 60 matches and I see so many players afraid to play and make mistakes and I don’t know why,” he added.
"My team in general receives very well. In these two matches we received so badly. Only at some points we played a good volleyball,” the Serbian coach added.