...In addition, Church said it's not clear whether limpet mines caused the explosions in either tanker. Limpet mines are usually attached by divers to the hulls of ships at the water line. There have been some reports that crew members aboard one of the tankers saw a flying object, possibly a drone, heading toward the ship before the explosion occurred, raising the possibility that a drone delivered the explosives.

"Drones and limpet mines are a dime-a-dozen out there in the Middle East," he said. "Everybody has them. So we need to know a lot more that what the video shows us."

Church also says it's not clear why, in the latest attacks, Iran would target tanks belonging to Norway and Japan, two of Iran's best oil customers. "They've been shipping to these countries for decades," he said. "Why would they do that?" Church says an independent investigation of the attacks is needed to determine responsibility.

Cordesman, who believes the Iranians are probably behind the attacks, says under Iran's increasingly dire economic circumstances, attacking long-standing customers makes perfect sense. "You push your customers into realizing that their supplies are threatened and then have them react against the United States," he said. "So to get that reaction, you provoke it."

But even Cordesman can't say for certain who was behind the attacks.

"The truth of the matter is either you have evidence, or you don't," he said. "Is there hard evidence that Iran is guilty? The answer is no. But is it probable that Iran is guilty? I would say the answer is yes. But those are two very different things."