Majid Taheri — an Iranian-American who had been working at a clinic in Tampa, Florida — had been detained in the United States for 16 months.
He was freed last Thursday as Iran released US navy veteran Michael White, who had been detained in the country since his arrest in July 2018.
Upon his arrival at Tehran’s Imam Khomeini International Airport, Taheri was greeted by Deputy Foreign Minister Hossein Jaberi Ansari.
State media published pictures of the pair speaking to journalists.
"I hope to see the release of [other Iranians imprisoned abroad] in the near future,” Ansari was quoted as saying by ISNA news agency, adding his ministry would do its best to achieve this.
Ansari said the scientist was freed after months of efforts by the ministry in coordination with Switzerland, whose embassy in Tehran handles US interests.
Taheri for his part thanked Iran’s Foreign Minister Mohammad Javad Zarif.
"I thank the government of the Islamic Republic of Iran and dear officials, including Mr Zarif, who worked hard, and other officials who took months to help release me, as an Iranian physician accused of circumventing US sanctions on medicine,” he was quoted as saying.
Taheri was the second scientist to have returned to Iran from the United States in the past week, after Cyrus Asgari flew home on Wednesday.
‘Unfair and false’
A US federal judge issued an order to free Taheri on time served.
Taheri had been accused of violating US sanctions by sending a technical item to Iran and in December pleaded guilty to charges he violated financial reporting requirements by depositing $277,344 at a bank, repeatedly showing up with loose cash, according to court documents.
Government spokesman Ali Rabiei called on the US to release all Iranians in its custody.
"We hope that this process of the full release of all Iranian prisoners in the United States will continue,” he said, quoted by ISNA.
"Iran is fully prepared to exchange all prisoners, and the US government is responsible for this procrastination.”
Taheri on Monday rejected accusations against him as "unfair and false”, according to Iran’s Fars news agency.
"I was helping the University of Tehran to develop a cancer vaccine, especially for women,” he was quoted as saying.
‘Maximum pressure’
Iran-US tensions have soared in recent years as President Donald Trump has pursued a campaign of "maximum pressure” against America’s sworn enemy.
Since unilaterally withdrawing the US from the Iran nuclear deal in May 2018, Trump has hit the Islamic republic with sweeping sanctions.
The two sides appeared to come to the brink of a direct conflict for the second time in less than a year in January, when Trump ordered an air strike that killed one of Iran’s top generals, Qassem Soleimani, in Baghdad.
Iran retaliated by firing a barrage of missiles at US troops in Iraq, but Trump opted against responding militarily.
While the attack on the western Iraqi base of Ain Al Asad left no American soldiers dead, dozens suffered brain trauma.
Following White’s release, Trump voiced hope for progress with Iran.
"Thank you to Iran, it shows a deal is possible!” he tweeted.
Iran and the US have at times swapped prisoners despite having had no formal diplomatic relations since 1980.
Tehran exchanged Washington Post reporter Jason Rezaian in January 2016 for seven Iranians held in the US, on the day the nuclear agreement had entered into force.
In December, Iran freed Xiyue Wang, a US academic, in exchange for scientist Massoud Soleimani.
Americans and dual nationals currently known to be held by Iran include Siamak Namazi, his father Baquer, and Morad Tahbaz.
Two others — Gholam Reza Shahini and Karan Vafadari — have reportedly been freed from custody on bail.
Most of the Iranians held in the US are dual nationals charged with evading sanctions by either exporting goods to Iran or using the US financial system