Iraq paid the autonomous Kurdistan region only around half its monthly share of the national budget in May as part of other spending cuts, the Iraqi finance minister said on Tuesday, potentially putting further strain on an oil exports deal.

The December deal was hailed as a breakthrough in a long-running dispute over exports between the federal government in Baghdad and Kurdish regional authorities, who want to sell oil on their own terms.

Both sides accuse each other of violations.

Finance Minister Hoshiyar Zebari said Baghdad had paid 508 billion dinars ($430 million) to the region in May as expenditure had been lowered across the board, and sought to play down any impact on the oil deal.

"All the amounts for all ministries and state departments have been lowered," Zebari said. "There are no negative effects on the deal: it is standing and still ongoing."

Under the deal, the Kurds committed to export 550,000 barrels per day (bpd) of oil in return for the reinstatement of budget payments to the region, which Baghdad slashed in early 2014.

Baghdad says the region has failed to hand over the volumes they agreed upon to state-run oil marketing firm SOMO. The Kurds say they have not received the monthly 1.2 trillion dinars to which they are entitled in the 2015 budget, and are threatening to sell more oil independently to make up for the shortfall.

The Kurds said they exported an average of 577,621 bpd via pipeline to Turkey in May, of which 448,889 bpd was handed over to SOMO.