The United States and Saudi Arabia have presented a united front to Iran and Syria, alerting Iran's leadership that patience over its alleged nuclear ambitions is wearing thin and warning Syrian President Bashar al-Assad that they will boost support to rebels unless he steps down.

John Kerry, the US secretary of state, was in Saudi Arabia on Monday on the latest leg of a nine-nation tour through Europe and the Middle East on his first overseas trip as Washington's top diplomat

In Riyadh on Monday, Kerry reminded Iran that US President Barack Obama has vowed not to allow Iran to get a
nuclear weapon and that he has kept all options, including military options,on the table to prevent that from happening.

The window of opportunity for a diplomatic solution "cannot by definition remain open indefinitely", Kerry said. "There is time to resolve this issue providing the Iranians are prepared to engage seriously on the P5+1 proposal.

But talks will not go on for the sake of talks and talks cannot become an instrument for delay that will make the situation more dangerous,'' he said.

Prince Saud al-Faisal, the Saudi Foreign Minister, whose country shares concerns with other Gulf Arab states about
increasing Iranian aggressiveness in the region, agreed.

"We hope that the negotiations will result in putting an end to this problem rather than containing it," he said,"taking into account that the clock is ticking and negotiations cannot go on forever."

In addition to Saud and the Saudi crown prince, Kerry met in Riyadh with the foreign ministers of Kuwait, Bahrain and Oman, all of whom are equally wary of Iranian intentions.

Assad denounced
In a joint news conference after the meeting Kerry and Saud told reporters that Assad had lost all claim to be Syria's legitimate leader.

Saud, whose country along with other Gulf states is widely believed to be supplying weapons to the Syrian rebels, said Saudi Arabia could not ignore the brutality Assad is inflicting on his people.

Saud also decried the fact that the Assad continued to get weapons from "third parties", a veiled reference to Russia and Iran, which have backed the regime through the conflict.

"Saudi Arabia will do everything within its capacity, and we do believe that what is happening in Syria is a slaughter, a slaughter of innocents'' he said. "We can't bring ourselves to remain quiet. Morally we have a duty.''

The Obama administration has resisted appeals from the Syrian opposition to provide it with weapons and ammunitions over fears that they could fall into the hands of Islamic hardliners who have gained support among Assad
opponents.

But Kerry sidestepped a question about whether the arms reportedly being supplied to the rebels by Saudi Arabia and others were a concern.

Instead, he criticized Iran, Hezbollah and Russia by name for giving weaponry to the Assad regime.