If the United States blocks Iran’s oil exports, Iran’s president threatened that his nation is prepared to shut the Straits of Hormuz, a critical shipping route and waterway for the world’s oil supplies, CNBC reported Tuesday.

Iranian President Hassan Rouhani told state television, “if someday, the United States decides to block Iran’s oil [exports], no oil will be exported from the Persian Gulf.”

In November the U.S. reimposed nuclear sanctions on Iran, targeting its energy sector and has reduced its exports by 1 million barrels a day.

According to CNBC, in 2015 some 18.5 billion barrels of crude oil, accounting for about one-third of all crude shipped overseas, passed through the critical waterway.

Rouhani’s threat was made as the U.S. has ordered a strike group associated with the aircraft carrier USS John C. Stennis to deploy to the Persian Gulf.

The Wall Street Journal reported Tuesday that military officials described the move as “a show of force against Iran.”

The carrier group would also be supporting U.S. and allied efforts against ISIS in Iraq and Syria, and against the Taliban in Afghanistan.

Officials told the Journal that the presence of the carrier in the Gulf “certainly provides a deterrence” against any possible hostile Iranian actions.

It wouldn’t be the first time that Rouhani, often described as a moderate, has threatened the world’s oil supply routes.

In July, Rouhani, who is often described as a moderate, suggested that Iran would close the Straits of Hormuz, if the United States forced nations to stop buying Iranian oil. In a statement published at his website, Rouhani said, “The Americans have claimed they want to completely stop Iran’s oil exports. They don’t understand the meaning of this statement, because it has no meaning for Iranian oil not to be exported, while the region’s oil is exported.”

Islamic Revolutionary Guard Corps-Quds Force Commander Qassem Soleimani praised Rouhani for his comments. Referring to Rouhani’s statement, Soleimani said, “Your valuable statement that said there will be no guarantees for oil exports from this region unless the Islamic Republic of Iran (can) also export its oil was a source of pride.”

The Houthis, the Iranian-backed rebels in Yemen, have been threatening ships in the Bab al-Mandab straits, at the mouth of the Red Sea. The Houthi threat prompted Israeli Prime Minister Benjamin Netanyahu to assert earlier this year that an international coalition, including Israel, would be prepared to keep that critical waterway open.