An ax murder. Then, jail time. Sounds like a morbid crime story.

Yet this tale has taken a sudden and unexpected twist: The killer got a pardon and a hero's welcome.

That has stirred fears of a war.

The parole has exacerbated long-standing tensions over disputed land between Armenia and Azerbaijan, former Soviet republics that are nestled in the Caucasus region near Turkey, Iran and Russia.

The nations fought a war two decades ago over the region of Nagorno-Karabakh, now occupied by Armenia but surrounded and claimed by Azerbaijan.

A return to warfare could suck in world powers, analysts warned Wednesday. Thomas de Waal, an expert on the Caucasus with the Carnegie Endowment for International Peace, told CNN world energy markets would be disrupted in a conflict since an oil and a gas pipeline carrying Caspian oil curves around the conflict zone in Azerbaijan.

The ax killing happened in 2004 at a NATO center in Hungary, where troops from Armenia and Azerbaijan were getting training. Ramil Safarov, a soldier from Azerbaijan, killed Armenian officer Gurgen Margarian. Both men were studying English.

Safarov was sentenced to life in prison in Hungary, but that country recently extradited him to Azerbaijan with the understanding that he would serve at least 25 years of the sentence.

Not long after Safarov arrived in Azerbaijan, though, Azerbaijani President Ilham Aliyev pardoned him.

Armenians recoiled at what happened next: The killer got an apartment and a promotion.

"Mr. Safarov has been glorified in Azerbaijan as a national hero at all levels -- including the top level," said Zohrab Mnatsakanian, Armenia's deputy minister of Foreign Affairs. "This is a blow to the conscience of Europe, to the civilized world."

Azerbaijan's Foreign Affairs Ministry said on Twitter that the "issue must be considered in the context of aggression and ethnic cleansing against Azerbaijan by Armenia."

The United States, meanwhile, was among those nations objecting to the pardon. It expressed "deep concern" and asked Hungary for more information on why it extradited Safarov.

"We are communicating to Azerbaijani authorities our disappointment about the decision to pardon Safarov," a spokesman for the National Security Council, Tommy Vietor, said in a statement the White House released. "This action is contrary to ongoing efforts to reduce regional tensions and promote reconciliation."

Sabine Freizer, director of the International Crisis Group's Europe program, said world powers have taken note.

"There is an awareness among government officials, both in the United States, Russia, and among European officials, that this conflict is getting worse. There should be something done to stop it," Freizer said.

"This takes us a whole step downward," said the Carnegie Endowment's de Waal.

The tensions over Nagorno-Karabakh reflect strong cultural attachments for both peoples, what Sergey Markedonov, visiting fellow of the Russia and Eurasia Program at the Center for Strategic and International Studies, likens to a "Jerusalem for both societies."

Animosities over the disputed territory have simmered since the end of World War I. The Soviet Union's collapse in the 1990s triggered a war from 1992 to 1994 that killed 22,000 to 25,000 people and uprooted more than a million others.

The war ended "with a shaky truce," the International Crisis Group said.

The disputes between the countries over Nagorno-Karabakh and other territories remain an "unresolved conflict of the Soviet period," Freizer said. Amid the creation of newly independent countries after the Soviet collapse, she said, "no one was focused on the conflict."

"The kind of support for Yugoslavia," whose breakup led to major wars in Bosnia and Kosovo, was "never given to this region."

Over the years, violence has flared. Both countries occasionally talk tough about each other. And Azerbaijan's oil and gas wealth is making its way into the budget for a military preparing for war, Freizer said.

"Since 2011, we feel the situation has gotten worse," Freizer said.

The killer's pardon prompted a certain outrage factor, she said.