Iran says it is opening a new naval base on the eastern part of the strategic waterway at the mouth of the Gulf.
The state news agency, IRNA, quoted Admiral Habibollah Sayyari as saying that the base on the Strait of Hormuz would allow Tehran to block the entry of any "enemy" into the Gulf.
About 40 per cent of the world's oil passes through the strait.
Iran has warned that it would close the narrow strait if the US attacked it over its disputed nuclear programme.
The base is in the port of Jask, about 1,700km south of the capital, and it was inaugurated on Tuesday.
In a separate development, IRNA said Iran had opened an international aviation fair on the Gulf island of Kish.
The news agency said more than 20 foreign companies or their domestic representatives and local companies are participating in the four-day show.
It said participants came from countries such as Britain, Germany, France, Russia, China and Poland, but did not give any names.
Karim Aghai, the director of Kish airport, said about 80 light and ultra-light aeroplanes were on display.
It is the fourth exhibition since 2002 by Iran to attain knowledge, equipment and spare parts regarding its aging passenger fleet.
The industry has been hindered since US sanctions banned the export of advanced technology to Iran.
Meanwhile, Dmitry Medvedev, Russia's president, slammed as "short-sighted" US sanctions on Russia's main arms firm over the alleged sale of sensitive military technologies to Iran.
Rosoboronexport was one of 13 firms placed on a US state department blacklist last week under the Iran, North Korea and Syria Non-Proliferation Act.
Speaking on Tuesday, Medvedev said: "It is unfair competition - simply an attempt to cut off suppliers. We consider such sanctions as short-sighted."
The president said, however, that Russia will "practically not feel" the sanctions, which ban any US government body from doing business with the Russian company and have also targetted firms from China, Syria and Venezuela.
The US says the sanctions are meant to punish the firms for sales that have "potential to make a material contribution to the development of weapons of mass destruction or cruise or ballistic missile systems".
On Friday, Sergei Lavrov, Russia's foreign minister, described Washington's move as "inadmissible" and warned the sanctions would affect talks between world powers on Iran's nuclear programme.