While Votel said the scope of the recent Iranian maritime exercise was similar to that of other exercises done in the region, its timing gave it added significance.
Washington has promised further sanctions for November, directly targeting Iran's oil and gas exports, if Tehran does not meet its demands regarding uranium enrichment and supporting terror.
Iran's foreign minister Javad Zarif turned the tables on Washington's efforts to isolate the regime, saying Monday that it is in fact the US, Israel, and Saudi Arabia who are isolated in their hostility towards Iran.
"It's pretty clear to us that they were trying to use that exercise to send a message to us that as we approach the period of the sanctions here that they had some capabilities", US Central Command head General Joseph Votel told Pentagon reporters.
North Korea has been pursuing its weapons programmes in defiance of UN Security Council resolutions and sanctions.
Meanwhile, Iranian Foreign Minister Mohammad Javad Zarif said his country will not oppose third-country mediation between the US and Iran.
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The arrival of North Korea's foreign minister in Tehran just hours after Donald Trump had reinstated sanctions against Iran was "no coincidence", analysts believe, and is created to send the message that Pyongyang is reinforcing its alliances as denuclearisation talks with the United States stall.
Trump said Tuesday that anyone doing business with Iran will not be allowed to maintain business ties with the United States.
"The U.S.is considered an uncertain and unaccountable country in the world that does not comply with its commitments", he said.
Sanctions going forward are likely to continue that trend, with the U.S. looking to cut off as much of Iran's worldwide commerce as possible, and having no problem harming European business interests in the process.
President Trump pulled out of the nuclear deal in May, calling it "disaster".
US President Donald Trump pledged on Tuesday to prevent companies with business dealings with Iran from dealing with the United States.
In a climbdown from the strong language in its new legislation, the commission said it wouldn't take any action against firms flouting their warnings not to comply with United States sanctions.
Pompeo: Sanctions to be enforced until Iran 'behaves like a normal country'
Zarif continued, "Trump Administration wants the world to believe it's concerned about the Iranian people". European foreign ministers said Monday they "deeply regret" the reimposition of USA sanctions.
As the US move also puts Turkey in a tight situation, the Turkish foreign ministry said authorities are working to avoid the USA sanctions from harming Turkey.
The Syrian Foreign Ministry condemned Washington as well, saying that Syria supports Iran in the face of the "aggressive" US policies.
"North Korea's strategic policy is to deepen relations with the Islamic Republic of Iran and confront unilateralism", he said.
Chinese State Councilor and Foreign Minister Wang Yi said in Singapore on Friday that China is willing to work with all parties to continue safeguarding the Iran nuclear deal.
"In the current situation, friendly countries should develop their relations and cooperation in (the) global community", he told Ri Yong Ho, adding the two countries have "always had close views".
Trump brought back the punishing sanctions after unilaterally pulling out of a landmark 2015 deal between Tehran and Western powers to halt Iran's nuclear ambitions.
Iran's national flags are seen on a square in Tehran February 10, 2012, a day before the anniversary of the Islamic Revolution.
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