US president Donald Trump has warned Iran will face "new and serious consequences" unless all unjustly detained American citizens are released and returned.
Mr Trump urged Tehran to return Dubai-based Iranian-American businessman Siamak Namazi and his father, Baquer, who in October last year were sentenced by an Iranian court to 10 years in prison for espionage, the White House said on Friday. The US president also demanded the release of Robert Levinson, an American former law enforcement officer who disappeared more than 10 years ago in Iran.
Iran responded on Saturday by demanding that the United States release Iranian detainees.
"The statements of the White House, as usual, are an example of interference in Iran's internal affairs and the demands are unacceptable and rejected," Iranian foreign ministry spokesman Bahram Qassemi said, according to the Iranian Students' News Agency.
The White House statement on Friday capped a week of rhetoric against Tehran. On Tuesday, Washington slapped new economic sanctions against Iran over its ballistic missile programme and said Tehran's "malign activities" in the Middle East undercut any "positive contributions" coming from the 2015 nuclear accord.
Those measures signalled that the Trump administration was seeking to put more pressure on Iran while keeping in place an agreement between Tehran and six world powers to curb its nuclear programme in return for the lifting of international oil and financial sanctions.
Friday's statement said Mr Trump and his administration were "redoubling efforts" to bring back all Americans unjustly detained abroad.
An Iranian court sentenced 46-year-old Siamak Namazi and his 80-year-old father Baquer Namazi to 10 years in prison each on charges of spying and co-operating with the United States.
Iran's Revolutionary Guard detained Siamak Namazi, 46, in October 2015 while he was visiting family in Tehran, relatives said.
The Revolutionary Guard then arrested Namazi's father, a former Iranian provincial governor and former Unicef official, in February last year after he arrived in Iran to seek his son's release, family members said. Baquer Namazi is 80 years old.
Levinson, a former agent for the Federal Bureau of Investigation and the US Drug Enforcement Administration, disappeared in Iran in 2007. The US government has a US$5 million (Dh18.4m) reward for information leading to his safe return.
On Sunday, Iran's court sentenced Xiyue Wang, a Chinese-born US citizen, to 10 years in jail on spying charges.
"Iran is responsible for the care and well-being of every United States citizen in its custody," the White House said on Friday.
Also on Saturday, Iran announced the launch of a new missile production line, according to state media.
The Sayyad 3 missile can reach an altitude of 27 kilometres and travel up to 120 kilometres, Iranian defence minister Hossein Dehghan said at a ceremony.
The missile can target fighter planes, unmanned aerial vehicles, cruise missiles and helicopters, he added.