A Government spokesperson said: "As part of our long-standing presence in the Gulf, HMS Duncan is deploying to the region to ensure we maintain a continuous maritime security presence while HMS Montrose comes off task for pre-planned maintenance and crew change over.
"This will ensure that the UK alongside international partners can continue to support freedom of navigation for vessels transiting through this vital shipping lane."
The US, who earlier this year deployed a carrier strike group and extra personnel to the region, has called for an international military coalition to help protect the Gulf's waters.
The Government stressed HMS Duncan's deployment is not in response to a request from the US or as part of a coalition force.
A Downing Street spokeswoman said they are "concerned" about threats Iran are making "to disrupt shipping in the area".
"We have been urging them to de-escalate the situation in the region," the spokesperson told a Westminster briefing.
Along with Montrose, the Navy has four mine countermeasures vessels and the Royal Fleet Auxiliary Cardigan Bay logistics ship in the region.