An Iranian court has upheld 10-year jail terms for an American, two US-Iranian dual nationals and a Lebanese resident of the United States who were convicted on charges of spying and collaboration against the state.

Tehran's prosecutor's office confirmed on Sunday that the four men's appeals had been rejected.

Prosecutor Abbas Jafari Dolatabadi identified the four as Princeton University student Xiyue Wang, Iranian-American businessman Siamak Namazi and his elderly father Baquer, and Nizar Zakka, a Lebanese citizen with permanent US residency, the judiciary's official news website reported.

Jared Genser, a US-based lawyer for the Namazis, said in a statement carried by US media last week that their family was informed that a Tehran court had upheld the convictions days earlier.

READ MORE: US urges Iran to free detained American citizens

Earlier in August, Princeton University and the wife of Wang, a history doctoral student and US citizen, said they had been informed that Iranian authorities had denied the appeal.

Wang was conducting dissertation research in Iran in 2016 when he was detained and charged with "spying under the cover of research", an accusation his family and university denied.

Iran sentenced Zakka, a Lebanese citizen with permanent US residency, to 10 years in prison and a $4.2 million fine in 2016 after he was found guilty of collaborating against the state, according to his US-based lawyer.

Zakka, an information technology expert, had been invited to Iran by a government official a year earlier, but then disappeared after attending a conference in Tehran.

'New and serious consequences'

The ruling comes at a time of rising tensions between Iran and the US following President Donald Trump's arrival in the White House.

In July, Trump warned that Iran would face "new and serious consequences" unless all "unjustly detained" American citizens were released and returned.

"We call for the immediate release of all US citizens unjustly detained in Iran so they can return to their families," a US Department of State official also said.

READ MORE: Out of sight - Imprisoned in Iran

"The Iranian regime continues to detain US citizens and other foreigners on fabricated national security-related charges," the official said.

"The safety and security of US citizens remains a top priority. All US citizens, especially dual nationals considering travel to Iran, should carefully read our latest travel warning."

The US warnings triggered criticism from Tehran of the detention of Iranian citizens in the US.

"You are keeping our innocent citizens in gruesome prisons. This is against the law and international norms and regulations," Sadegh Larijani, the head of Iran's judiciary, said.



"We tell them that you must immediately release Iranian citizens locked up in US prisons."



Iran's Foreign Minister Mohammad Javad Zarif also accused Washington of holding Iranians on "charges of sanction violations that are not applicable today ... for bogus and purely political reasons".

Dozens of arrests

Iran's 2015 nuclear deal with world powers lifted most international sanctions and promised Iran's reintegration into the global community in exchange for curbs on its nuclear programme.

But according to some experts, Iranian hardliners have been alarmed by the flood of European trade and investment delegations who have arrived in Tehran to discuss possible deals.

Security officials have arrested dozens of artists, journalists and businessmen, including Iranians holding joint American, European or Canadian citizenship, as part of a crackdown on "Western infiltration".

READ MORE: Iran charges dual nationals, foreigner in crackdown

The arrests have undermined President Hassan Rouhani's goals of reviving business and political ties with the West, as well as pushing for more political and social reforms at home, Iran experts and observers have said.

A number of Iranian dual nationals from the US, Britain, Austria, Canada and France have been detained in the past year and are being kept behind bars on charges including espionage and collaborating with hostile governments.

According to former prisoners, families of current ones, and diplomats, in some cases the detainees are kept to be used for a prisoner exchange with Western countries.

In January 2016, the United States and Iran reached a landmark prisoner swap deal that saw Iranians held or charged in the US, mostly for sanctions violations, released in return for Americans imprisoned in Iran.