(Adds Ban comment on military strikes in Iraq)
NEW YORK, June 20 (Reuters) - U.N. Secretary-General Ban Ki-moon urged the Security Council on Friday to impose an arms embargo on Syria, describing foreign powers and groups as "irresponsible" for giving military support to the warring parties in the three-year conflict.
In a speech on Syria at the Asia Society in New York, Ban also said: "I welcome recent contacts between Iran and Saudi Arabia and hope that they will build confidence and reverse a destructive competition in Syria, Iraq, Lebanon and elsewhere."
Ban expressed anger that the international community has been unable to find a way to end the civil war that has killed some 150,000 people, displaced half the country's 22 million population and forced nearly three million to flee.
International and regional powers have backed opposing sides, with Russia and Iran supporting Syrian President Bashar al-Assad and Western powers and Gulf Arab states largely backing the rebels. The U.N. Security Council has been largely deadlocked.
"Syria today is increasingly a failed state," Ban said. "The Syrian conflict has now spread visibly and devastatingly to Iraq, with flows of arms and fighters across a porous border."
He warned against airstrikes on militants in Iraq, who have seized the north of the country. He said military strikes "might have little lasting effect or even be counter-productive if there is no movement towards inclusive government."
Ban unveiled a six point plan to chart the way forward in Syria - end the violence, protect civilians, start a serious political process, ensure accountability, finish the destruction of Syria's chemical weapons and address the regional dimensions of the conflict, including the extremist threat.
"It is essential to stem the flow of arms pouring into the country. It is irresponsible for foreign powers and groups to give continued military support to parties in Syria that are committing atrocities," Ban said.
"I urge the Security Council to impose an arms embargo. If divisions in the Council continue to prevent such a step, I urge countries to do so individually. Syria's neighbors should enforce a firm prohibition on the use of their land borders and airspace for arms flows and smuggling into Syria," he said.
Russia, supported by China, has shielded Syria on the U.N. Security Council during the conflict by vetoing four resolutions that threatened action against Assad's government. Russia is also one of Syria's main arms suppliers.
The United States is supplying rebels with "non-lethal" aid - such as radios, trucks and training. But some U.S. officials say small arms and anti-tank missiles are also being given. (Reporting by Michelle Nichols; Editing by Chizu Nomiyama)