Iraqi Prime Minister Nuri al-Maliki has declined an invitation from his Turkish counterpart Recep Tayyip Erdogan to visit Ankara, the Iraqi premier's spokesman said on Thursday.

Maliki expressed regret that he could not accept the invitation, as "his schedule is crowded and he is busy," Ali Mussawi told AFP.

Ties between Iraq and Turkey have been marred by a flurry of disputes this year, most recently Ankara's refusal to extradite Iraqi Vice President Tareq al-Hashemi, who has been sentenced to death in absentia by an Iraqi court.

In August, Maliki accused Turkey of treating the autonomous Kurdistan region of north Iraq, with which it has close economic ties, as an "independent state."

Earlier that month, Turkish Foreign Minister Ahmet Davutoglu visited the disputed northern Iraqi city of Kirkuk without informing Baghdad, infuriating Iraq and taking relations to a new low.

In July, Iraq warned Ankara against "any violations" of its territory and airspace, and instructed the foreign ministry to register a complaint at the UN Security Council, after Turkish jets bombed Kurdish rebels in Kurdistan.

A few days earlier, Iraq called on Turkey to stop accepting "illegal" transfers of crude oil from Kurdistan, which an official from the region said had begun earlier in the month.

And in April, Maliki said Turkey was becoming a "hostile state" in the region, accusing Erdogan of interfering in internal Iraqi affairs.

His remarks came after the Turkish premier accused Maliki's Shiite-led government of stoking sectarian tensions.