An international flight ban enacted by the central Iraqi government against cities in Iraq's northern Kurdish region came into effect Friday evening amid rising tensions following Monday's controversial vote for Kurdish independence.

The ban took effect at 6 p.m. local time (1600 UTC) and covers all international flights to Iraqi Kurdistan's capital city, Irbil, and its second-largest city, Sulaimaniya. Domestic flights will continue as normal, the Iraqi ministry of transport said today.

Iraqi Prime Minister Haider al-Abadi had announced on Wednesday that his government would institute the ban within three days if leaders from the Kurdistan Regional Government (KRG) did not hand over control of local airports to Iraqi authorities.

The KRG refused to meet that demand and has criticized Baghdad for pursuing "unlawful" measures that amount to "collective punishment."

"The Irbil and Sulaimaniya airports belong to Kurdistan," KRG Transport Minister Mawlood Bawa Murad said Wednesday. "The demand of the Iraqi government to hand over airports is inappropriate and incorrect."

Read more: Iraq warns Kurds as they claim victory in independence vote

KRG leader Massud Barzani had called on the central government to join negotiations about Kurdistan's future after more than 90 percent of Kurdish voters opted for secession on Monday. Baghdad should "not to close the door to dialogue because it is dialogue that will solve problems," Barzani said Tuesday.

Most regional and several international carriers have said they will halt flights to the region. Well-known airlines Egypt Air, Qatar Airways, Turkish Airlines, Lufthansa, and Austrian Airlines have all announced flight cancellations.

No oil, few friends

The KRG has found itself increasingly isolated as Baghdad and other neighboring countries with large Kurdish populations have pressed for the referendum result to be annulled.

Turkey said Thursday that it would start dealing exclusively with Baghdad on oil sales. The KRG could lose up to 80 percent of revenue if Turkey decides to halt imports of Iraqi oil via a pipeline that runs through Iraqi Kurdistan.

Turkish Prime Minister Binali Yildirim has said however that Ankara would only institute targeted oil sanctions against individuals responsible for holding the referendum to avoid impacting civilians in the region. He did not give further details on how the sanctions would spare civilians.

Turkey is home to the largest Kurdish population in the region and Ankara fears that Monday's vote may bolster Turkish Kurds' calls for independence. Turkish President Recep Tayyip Erdogan has warned that any move toward independence would risk an "ethnic war."

Read more: Opinion: Kurds find few friends in independence referendum

Both Turkey and Baghdad have signaled a willingness to intervene militarily in the KRG if Kurdish leaders do not back down.

On Wednesday, the Iraqi parliament asked Prime Minister al-Abadi to use the Iraqi army to retake the oil fields in Kirkuk, an area that the KRG has only controlled since 2014, but that it included in the independence referendum.

The prime minister has so far held off sending troops into the area. However, the Iraqi military has conducted joint military drills with Turkey along the Iraqi Kurdistan border and Baghdad has said it also sent a delegation to Iran, which also opposes Kurdish independence, "to coordinate military efforts."

Turkey and Iran have also reportedly conducted joint military exercises along their respective borders with the KRG.

The US, the European Union, and the United Nations have all criticized the referendum, saying it risks destabilizing an already volatile region.

Read more: The Middle East's complex Kurdish landscape

amp/kms (AP, Reuters, dpa, AFP)