Iran has arrested 12 people it claims were working undercover for the CIA inside the Islamic republic, further raising tensions in its already strained relationship with the US.

On Wednesday, the Irna state news agency quoted a senior Iranian official as saying that the spies it claimed to have arrested had been gathering intelligence from Iran's security and military units as well as its highly sensitive nuclear programme.

"The main mission of this act of espionage was related to Iran's progress in the fields of nuclear technology and also military and security activities," said Parviz Sorouri, a member of the parliamentary committee on national security and foreign policy, in quotes carried by Irna.

Sorouri told the agency that the network had been uncovered by an operation involving the Iranian ministry of intelligence. "The US and Zionist regime's espionage apparatuses were trying to damage Iran both from inside and outside with a heavy blow, using regional intelligence services," he said. "Fortunately, with swift reaction by the Iranian intelligence department, the actions failed to bear fruit."

Sorouri's comments follow reports on Monday that Iran and the Lebanese Shia militia, Hezbollah had identified alleged CIA informants.

The leader of Hezbollah, Hassan Nasrallah, said in June that his group had uncovered at least two CIA informants within its ranks but his claims were met with scepticism at the time. But former US officials told Reuters this week that those arrested were indeed working for the CIA. The officials claimed the agents were "believed to be local recruits" working for the CIA rather than US citizens.

Iran did not specify the nationality of the individuals it has arrested and the CIA has declined to comment on the recent reports, saying "it does not, as a rule discuss allegations of operational activities".

In October, tensions between Tehran and Washington escalated after US authorities said military factions inside the regime have conspired to kill the Saudi ambassador to Washington. Iran denied the allegations and one Iranian diplomat told the Guardian that the US had resorted to a so-called "entrapment technique" in order to smear Tehran in the eyes of the international community. US allegations were met with widespread scepticism because of the sloppy nature of the alleged assassination plot and the limited evidence provided by the US.

In a tit for tat reaction in November, Iranian officials accused the US of committing acts of terrorism in the Islamic republic. Iran said at the time that it had evidence showing the US had been behind "terror" operations in Iran, including the assassination of its nuclear scientists.

"We have 100 unbeatable documents on the US role in directing terror and terrorists in Iran and the region," the supreme leader, Ayatollah Ali Khamenei claimed. "By releasing these documents, we will dishonour the US and those who claim to be the advocates of human rights and campaign against terrorism among the world public opinion." Iran claimed it had sent the documents to the UN but has so far not provided them to the media.

In recent years, Iran's nuclear programme has experienced a series of dramatic setbacks after the assassinations of its scientists and the Stuxnet computer worm, which was designed to sabotage its atomic facilities and halt its uranium-enrichment programme. This month, an explosion at a military base near Tehran killed the architect of Iran's missile programme. Iran has pointed the finger at the US and Israel for what has been widely seen as a covert war against the country's nuclear programme and military capabilities.