TEHERAN: Four tankers caught fire after hitting mines while attempting to navigate the Strait of Hormuz, Iran's armed forces said on Thursday, a day after the US military said it had cleared key routes through the waterway.

"Over the past 24 hours, three violating oil tankers exploded and caught fire after striking mines while attempting to pass through the unauthorised southern route of the Strait of Hormuz," Iran's Islamic Revolutionary Guards Corps (IRGC) said in a statement.

Later on Thursday, Iran's army reported that another tanker had caught fire east of the strait after hitting mines while "operating in a restricted and dangerous area".

The initial three vessels had "switched off all their radar and navigation systems" and disregarded warnings from the IRGC navy, the statement said.