MANAMA - Iran has built up its naval forces in the Gulf and prepared boats that could be used in suicide attacks, but the US Navy can prevent it from blocking the Strait of Hormuz, the commander of US naval forces in the region said on Sunday.Iran has made a series of threats in recent weeks to disrupt shipping in the Gulf or strike US forces in retaliation if its oil trade is shut down by sanctions, or if its disputed nuclear program comes under attack."They have increased the number of submarines ... they increased the number of fast attack craft," Vice Admiral Mark Fox told reporters. "Some of the small boats have been outfitted with a large warhead that could be used as a suicide explosive device. The Iranians have a large mine inventory.""We have watched with interest their development of long range rockets and short, medium and long range ballistic missiles and of course ... the development of their nuclear program," Fox, who heads the US Fifth Fleet, said at a briefing on the fleet's base in the Gulf state of Bahrain.