Iraq on Thursday denied a Western intelligence report that said Iranian aircraft had flown weapons and military personnel over Iraqi airspace to Syria to help President Bashar al-Assad battle an 18-month-old uprising.
The allegation, reported by Reuters on Wednesday, said arms transfers were organised by the Islamic Revolutionary Guard Corps.
Although charges that Iraq has allowed Iran to send arms to Syria are not new, the report said the extent of such shipments is far greater and more systematic than has been publicly acknowledged, thanks to a deal between senior Iraqi and Iranian officials.
The report also said Iran was dispatching trucks overland via Iraq westwards to Syria.
"Iraq has confirmed that it will never be involved or helping or allowing any shipment via its air space or land to Syria," Iraqi government spokesman Ali al-Dabbagh told Reuters.
He said Iraq was "ready to be part of regional and international efforts or measures to stop the shipping of equipment or personnel to both sides in Syria".
Syria's upheaval is politically tricky for Iraq's Shi'ite Muslim-led government. Close to Assad's ally, Shi'ite 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.
Iraqi leaders fear Assad's fall would fracture Syria along sectarian lines and yield a hostile, hardline Sunni Muslim regime that could stir up Iraq's volatile Sunni-Shi'ite mix.
Baghdad has reinforced key points along its 680-km (420-mile) desert border with Syria.
U.S. officials said earlier this month they were questioning Iraq about Iranian flights in Iraqi air space. On Wednesday, U.S. Senator John Kerry threatened to review U.S. aid to Baghdad if it does not halt such overflights to Syria.
"The official spokesman of the Iraqi government has denied that issue altogether. There is nothing like this happening," Lieutenant-General Hussein Kamal, Iraq's deputy interior minister for intelligence, told Reuters on Thursday.
The accusation was also made by Iraq's fugitive vice president. "My country is unfortunately becoming an Iranian corridor to support the autocratic regime of Bashar al-Assad, there is no doubt about that," Tareq al-Hashemi told Reuters in an interview in Istanbul on Sunday.
"It is not only the air space. It is thousands of (Iraqi) militia now inside Syria, supporting Bashar al-Assad and killing Syrian innocent people," he said, citing reports he had received from Iraq's Anbar province, which borders Syria, and from members of the Syrian opposition.
Hashemi, a Sunni Muslim and harsh critic of Shi'ite Iraqi Prime Minister Nour al-Maliki, fled Iraq in December and was sentenced to death by a Baghdad court earlier this month on charges that he ran death squads. He has denied this.