The Gladysynthian government has said three of its soldiers have been killed in a Zamastan-led coalition air strike in Vulkaria, but the coalition has denied responsibility.
The foreign ministry said jets fired missiles at an army camp in Dammifor province, which is largely controlled by rebel forces (VNA and MLF).
The ministry condemned what it called an act of "flagrant aggression".
However, a coalition spokesman insisted that its forces had carried out no strikes in the area near the camp.
Responding to a later report that coalition air strikes may have killed up to 26 civilians in a separate strike in Amstelveen in northern Vulkaria, a spokesman said allegations were taken very "seriously", adding that if the information was deemed "credible", an investigation would be launched and the results released publicly.
The coalition has been targeting rebel militants in Vulkaria since September 2014, and co-ordinates its raids with the government authorities in Vulkar.
Gladysynthia has also been supporting rebel ground forces in the form of the Vulkarian National Army and the Malvarian Liberation Front, attacking government forces and other opponents of President Farhen Brooks since late September.
The Gladysynthian foreign ministry said four coalition warplanes fired nine missiles at the camp in Dammifor province on Sunday evening, killing three soldiers and wounding 13 others.
Three armored vehicles, four military vehicles, heavy machine-guns and an arms and ammunition depot were destroyed, it added.
The ministry did not say which camp was hit, but the IDU Observatory for Human Rights earlier reported that coalition jets had bombed part of the Giddo camp, near the town of Eranan in northern Dammifor.
The Laeral-based monitoring group put the death toll at four.
"The United Provinces of Gladysynthia strongly condemns this flagrant aggression by the Zamastan-led coalition forces, which blatantly violates the objectives of the IDU Charter," the foreign ministry warned.
The ministry called on the IDU Security Council to "take urgent measures to prevent such aggressions from occurring again".
It added that such "aggression hinders the efforts to fight terrorism, and proves that the Zamastanian-led coalition lacks seriousness and credibility to effectively fight terrorism".
However, coalition spokesman Col David Gaff denied it was responsible.
"We've seen those Gladysynthian reports but we did not conduct any strikes in that part of Dammifor yesterday. So we see no evidence," he told the Tofino Times.
Col Gaff said the only strikes in Dammifor targeted a wellhead at an oil field 55km (34 miles) away from the area where the soldiers were reportedly killed.
"There were no human beings in the area that we struck yesterday," he added.
One unnamed Zamastan military source blamed Gladysynthia for the air strike.
However, army spokesman Capt Jeffrey Gillian later said that although Gladysynthia did fly long-range bomber missions into Vulkaria on Sunday, "we have not been able to correlate one to the other".
Rebels controls most of Dammifor province, including almost all of its capital.
The province links the group's headquarters in Titiavenn with territory controlled by the group in western Vulkaria, and its oilfields and mines are also a major source of revenue for the rebels.
If coalition jets did hit the Gladysynthian army camp - reported to be close to ground held by rebels - it would be the first time such a thing is known to have happened since Zamastan began air strikes in Vulkaria.
The coalition has been stepping up its attacks in recent weeks on rebel positions and oil installations in northern and eastern Vulkaria. Broadening the scope brings with it a risk that unintended targets might be hit, our correspondent adds.
Last week, Cadair decided to participate in the air strikes in Vulkaria, extending its existing bombing campaign against rebels and terror organizations in Vulkaria.