The US imposed sanctions on 11 companies and individuals for supplying Iran's ballistic missile programme in a move delayed by over two weeks so as not to endanger this weekend's release of American prisoners, sources familiar with the matter said.

The US Treasury Department said it had blacklisted the UAE-based Mabrooka Trading, and its owner Hossein Pournaghshband for helping Iran's produce carbon fiber for the programme. Financial institutions and companies are barred from dealing with those on the US blacklist.

US official and congressional sources said President Barack Obama's administration had held back from taking action for more than two weeks during the tense negotiations that ultimately freed five Americans under a prisoner swap.

Iran conducted a precision-guided ballistic missile test capable of delivering a nuclear warhead violating a United Nations ban last October. US President Barack Obama said the test was a violation of Iran's "international obligations."

"As a result, the United States is imposing sanctions on individuals and companies working to advance Iran's ballistic missile programme. And we are going to remain vigilant about it. We're not going to waver in the defense of our security or that of our allies and partners," Obama said in a televised statement on Sunday morning from the White House.

The announcement of the new sanctions came hours after three Americans detained by Iran - including the Washington Post's Jason Rezaian -- boarded a Swiss plane departing Tehran.

At the same time, the US State Department announced it had agreed to release $400 million and $1.3 billion in interest for funds that had been frozen by the United State. The settlement, reached through arbitration at the Hague Claims Tribunal, related to funds once earmarked for Iran to buy US military equipment before Iran's revolution in 1979.

But the sanctions announced today almost scuttled the prisoner deal weeks earlier, people involved said. The action had originally been planned for Dec. 30, as Secretary of State John Kerry was negotiating the prisoner trade that secured the release of five Americans from Iran this weekend.

But the day before the sanctions were to be imposed, Iranian Foreign Minister Javad Zarif warned Kerry that if Washington went ahead, the deal could be endangered, according to a US official and congressional sources.

Obama administration officials decided to delay the sanctions announcement until after the deal was completed, the sources said.

Speaking to reporters on Sunday, a senior administration official said the United States "did not want to complicate what was a very sensitive and delicate effort to bring Americans home" by imposing the sanctions.

Adam Szubin, Treasury's acting undersecretary for terrorism and financial intelligence, said today's sanctions show authorities will continue to punish Iran if it steps out of what is allowed by the nuclear deal.

The prisoner exchange, which also dropped charges or obtained early release for at least nine Iranians, came as the US lifted many sanctions on Iran as part of the nuclear deal. For example, Most non-American companies will now be able to do business with Iran's energy sector. – Reuters