(CNN) US national security adviser John Bolton blamed Iran on Wednesday for the attack on four oil tankers at a port in United Arab Emirates this month, without offering evidence that Tehran was responsible.

"I think it is clear these (attacks) were naval mines almost certainly from Iran," Bolton told reporters during a visit to Abu Dhabi on Wednesday.

Iran later rejected Bolton's claim as "ridiculous" that it was responsible for the May 12 attack on the four oil vessels near the Emirati port of Fujairah.

Bolton also said Wednesday that the additional 1,500 US troops sent to the Middle East region are to "act as a deterrent" against Iranian threats. The Trump administration has also sent a carrier and bomber task force to the Persian Gulf.

"The point is to make it very clear to Iran and its surrogates that these kinds of actions risk a very strong response from the United States," he said.

Read More