Vice President Joe Biden discussed with Iraqi Prime Minister Nouri Al-Maliki Friday the need to prevent Iraqi territory and airspace from being used to ship weapons to Syria, the White House said, amid allegations of an illicit arms flow from Iran.

It was the highest level contact between Washington and Baghdad on the issue, following a Western intelligence report that Iranian aircraft had flown weapons and military personnel across Iraqi airspace to Syria to aid President Bashar Al-Assad's efforts to crush an 18-month popular uprising.

Iraq denied the allegation Thursday. The report said the flights had been organised by Iran's Revolutionary Guard Corps. Iran is a staunch ally of Al-Assad.

US officials said earlier this month they were questioning Iraq about Iranian overflights. On Wednesday, US Senator John Kerry threatened to review US aid to Baghdad if it does not put a halt to such flights.

"The vice president and the prime minister addressed issues of regional security, including the need to prevent any state from taking advantage of Iraq's territory or air space to send weapons to Syria," the White House said in a summary of the leaders' wide-ranging discussion.

But the statement stopped short of accusing Iraq's Shia Muslim-led government of collaborating with Shia Iran. Baghdad has resisted joining Western and fellow Arab calls for the Syrian leader to step down while also calling for a reform process in Syria.

Tehran is forbidden from selling weapons under a UN arms embargo that is part of broader sanctions against Iran over its nuclear programme.