BAGHDAD, Iraq (CNN) -

Reports that Syrian warplanes carried out a cross-border attack on Iraqi towns this week is further evidence of the blurring between the two countries' borders as they face an offensive by Islamic extremists.

At least 57 Iraqi civilians were killed and more than 120 others were wounded by what local officials say were Syrian warplanes that struck several border areas of Anbar province Tuesday.

These border cities are among those under the control of the Islamic State in Iraq and Syria, or ISIS, which seeks to create an Islamic caliphate that encompasses portions of Iraq in Syria.

Reports of the Syrian incursion into Iraq is a reminder that the civil war in Syria and the unrest in Iraq are not isolated, but linked in ways that threaten the security of both.

Sabah Karkhout, head of Iraq's Anbar provincial council, told CNN that Tuesday's air attacks struck markets and fuel stations in areas such as Rutba, al-Walid and Al-Qaim.

"Unfortunately, (the) Syrian regime carried out barbarian attacks against civilians in Anbar province," he said Wednesday.

Karkhout said he was certain the warplanes were Syrian because they bore the image of the Syrian flag.

"Also, the planes flew directly from Syrian airspace and went back to Syria," he said.

Local officials said residents used scopes and other equipment to see details on the warplanes.

Iraq's military spokesman, Maj. Gen. Qassim Atta, denied reports that Syrian warplanes struck inside Iraq's border towns.

"We know our airspace. We have not recorded or registered infiltration of our air space from foreign jets, and all the warplanes and helicopters flying over Iraq airspace are Iraqis," he told CNN.

The head of the United Nations Assistance Mission for Iraq, Nickolay Mladenov, told reporters Wednesday that the warplanes that bombed the Iraqi cities were not Iraqi jets, but he did not have information beyond that.

Syrian state media called the reports of a cross-border incursion "completely baseless" allegations made by "malicious media outlets," citing a "Syrian media source."

CNN is seeking a response from the Syrian government in Damascus.

Iraq's border region has been targeted by Syria in the past -- as the Syrian conflict escalated in 2012, there was at least one instance where rockets fired from Syria landed in Al-Qaim.

Iraq's Foreign Ministry said at the time that it was ready to respond in the event of additional attacks from Syria, but the Iraqi government was noticeably quiet after Tuesday's incursion.

The claims come as Iraqi forces continue fighting radical Sunni militants from ISIS.

Inside Syria, the government, for the most part, appears to have avoided directly targeting ISIS, even though the group's positions are well known. Only in the last week did the Syrian regime intensify strikes on Raqqa, a city in Syria's interior that is considered ISIS's headquarters.

Warplanes carried out seven raids on Raqqa on Wednesday, killing at least 12 people, including a woman and child, the opposition Syrian Observatory for Human Rights said.

Whether the strikes signify a concerted effort by Syria to intensify its fight against ISIS is yet to be seen. It is also unclear whether the Syrian strikes in Iraq were a unilateral action or were coordinated with the Iraqi government.

Al-Maliki slams Sunnis

The sectarian rift in Iraq may have widened Wednesday when Iraqi Prime Minister Nuri al-Maliki blamed his political rivals for "coordinating" the crisis.

Al-Maliki, a Shiite, accused Sunnis of collaborating with militants and slammed the call to have a national salvation government that would remove him from power.

"Iraq is facing a cross-border terrorist attack that is supported by some neighboring countries," al-Maliki said in a televised speech.

He appealed to his Shia constituency by saying he is adhering to the wishes of Shiite religious leader Ali Sistani, who called for volunteers to support the Iraqi army and government.