Iran has carried out secret tests of missiles capable of delivering a nuclear payload in breach of UN resolutions, British Foreign Secretary William Hague said Wednesday.

Hague's comments came a day after Iran's elite Revolutionary Guards said they had fired 14 missiles in an exercise, one of them a medium-range weapon capable of striking Israel or US targets in the Gulf.

In a statement to lawmakers, Hague said: "Iran has also been carrying out covert ballistic missile tests and rocket launches, including testing missiles capable of delivering a nuclear payload in contravention of UN resolution 1929."

He said Iran had also announced plans to triple its capacity to produce 20 percent enriched uranium, adding: "These are enrichment levels far greater than is needed for peaceful nuclear energy.

"We will maintain and continue to increase pressure on Iran to negotiate an agreement on their nuclear programme," including sanctions, he said.

On Tuesday US State Department spokeswoman Victoria Nuland said Iran was "bragging" about its assets, but did not specify whether Washington thought the tested missiles were nuclear-capable.

Iran's missile programme, which is under the control of the powerful Guards along with its space projects, has been a mounting source of concern in the West.

Western governments fear Tehran is seeking to develop a ballistic capability to enable it to launch atomic warheads under cover of its civil nuclear programme.

Tehran denies any such ambition.