Iran refused to allow a plane carrying Iraqi Prime Minister Nuri al-Maliki to cross its air space overnight, a senior adviser to the Iraqi leader said on Sunday. Sadiq al-Rikabi, who is accompanying Maliki on the trip to Japan and South Korea, said the Prime Minister's plane entered Iranian air space on Saturday night.“Suddenly the Iranian aviation authorities ordered the pilot to go back,” Rikabi said. "We were obliged to fly to Dubai where we stayed for more than three hours,” he said. Rikabi said it was unclear why Iran had barred Maliki's plane from crossing its territory. Asked about the reports, Iranian Foreign Ministry spokesman Mohammad Ali Hosseini implied Maliki's plane may have faced an issue over permission to fly across Iran but said it was not an unusual problem. “Permission for Maliki's flight is a normal issue. All flights need permission," he told a weekly news conference in Tehran, without giving further details.Iraq's US-backed government has often had to tread a delicate path in trying to maintain good relations with both Iran and the US. Maliki, a Shi'ite, visited Tehran last September to urge Iran not to interfere in Iraq. Meanwhile, Iran today said any suspension of sensitive nuclear activities was not open to discussion, a day before President Ahmadinejad is expected to announce a major development on its atomic drive.