WASHINGTON (AFP) - A large majority of US House of Representatives members wrote to Secretary of State John Kerry expressing their concern on Thursday over Iran's "refusal" to work with the United Nations nuclear watchdog.

With a November deadline fast approaching for Teheran and world powers to reach a deal on the Islamic republic's nuclear programme, 354 of the House's 435 members warned that the International Atomic Energy Agency (IAEA) has been frustrated in its efforts to glean more information about the "potential military dimensions" of Iran's atomic efforts.

"We believe that Iran's willingness to fully reveal all aspects of its nuclear programme is a fundamental test of Iran's intention to uphold a comprehensive agreement," wrote the lawmakers including House Speaker John Boehner and several Democrats.

"We remain deeply concerned with Iran's refusal to fully cooperate with the (IAEA)," they added.

"The only reasonable conclusion for its stonewalling of international investigators is that Teheran does indeed have much to hide."

In a Sept 5 report, the IAEA accused Teheran of failing to fully respond to questions about its nuclear programme.

Iran had until Aug 25 to clarify five points laid out in an agreement with IAEA in May, but it has only initiated discussions on two of them.

The West believes Iran is seeking nuclear weapons capability, while Teheran insists its programme is for civilian use.

Congress has often expressed doubt about the negotiations between Iran and world powers Britain, China, France, Germany, Russia and the United States. A new round of nuclear talks will be held within the next two weeks, according to a senior Iranian official.

Some US senators tried this year to pass new sanctions that would enter into force if no final agreement is signed, but the effort failed amid opposition by President Barack Obama.