By SOLOMON MOORE

NAIROBI—Tensions rose between Ethiopia and Eritrea on Wednesday, after officials from the two hostile east African neighbors blamed each other for the killing of five European tourists along their border.

Ethiopian spokesman Bereket Simon said gunmen who carried out Monday’s attack in the Afar region of northeastern Ethiopia, about 25 kilometers from the Eritrean border, near the active Erta Ale volcano, were members of “subversive groups trained and armed by the Eritrean government.” He didn’t offer evidence to support his claim.

Eritrea’s foreign ministry called the accusation a “ludicrous” smear campaign, saying in a statement that Ethiopia has long been host to home-grown, armed opposition groups. Eritrean officials said the attack took place in Ethiopian territory, and is an Ethiopian matter.

A European official said a group of European tourists came under attack from an armed group between 1 a.m. and 5 a.m. local time on Monday. The official didn’t identify the armed group or its affiliation. Ethiopian and European officials said several of the tourists were taken captive.

A representative of Diamir Adventure Travel of Dresden, Germany, confirmed that the company had been involved, but declined to provide details of the attack, the number of travelers affected or the victims’ nationalities. European officials said the five dead included nationals from Germany, Austria and Hungary.

Twelve members of the tourist group had been rescued and were being flown by an Ethiopian helicopter to Addis Ababa, according to Theresa Schönfeld, a spokeswoman with Germany’s Foreign Ministry, who confirmed that at least two Germans were killed by gunmen.

Ms. Schönfeld said that she was relying on Ethiopian government sources for information about the attack.

The European officials said they still weren’t sure of the identities of all of the tourists Wednesday, and couldn’t say how many the gunmen still held captive. It was also unclear whether the tourists had been camping at the time of the attack, or hiking at night, as groups in the hot region sometimes do.

The incident has heightened frictions between two countries that bear intense ill will toward each other. The neighbors were one country until Eritrea declared its independence in 1993, fought a two-year border war that left tens of thousands dead, and have traded rhetorical barbs since the conflict ended in 2000. Both rivals have also backed armed groups inside strife-torn Somalia.

Wild and remote, the Afar region is among the hottest areas on earth. There are no roads, towns or cellular phone services in the vicinity. The site is best known for the discovery there, in 1974, of the remains of a 3.5-million-year-old human ancestor called Lucy.

Adventure travelers have also been drawn to a chain of lava lakes in the area. Dresden’s Diamir has led tours in the Afar region since 2006 without problems, said marketing director Thomas Mach. He said Diamir avoids regions identified in German travel advisories, but that the foreign ministry hadn’t issued such an advisory at the time of the attack.

Austria, however, had issued travel advisories for Afar since 2007, when five British Embassy staffers and 13 Ethiopians were kidnapped in the area. Ethiopian officials say their security forces averted an attempted attack on tourists in Afar in 2008. Land mines left over from the Ethiopia and Eritrea’s conflicts are also known to have harmed visitors in Afar.

“There’s been a valid travel warning specifically for this border region since 2007 on the basis of incidents over years been both politically and or criminally motivated, although we’re not sure who is being the attack this time,” said Austrian Foreign Ministry spokesman Peter Launsky Tiefenthal.

Among other issues, Ethiopia says Eritrea supports al Shabaab, the Islamist militia that controls vast tracts of Somalia, but Eritrea denies that.

The United Nations imposed an arms embargo on Eritrea in 2009 for its alleged support of al Shabaab. This week, the United Nations cleared Eritrea of accusations leveled by Kenyan officials that it recently sent air shipments of weapons to al Shabaab in order to help the Islamist militia fight African Union and Kenyan troops in Somalia. Eritrean officials renewed calls for an end to the embargo after the U.N. cleared the country of charges that it had air-dropped weapons in Somalia.

Ethiopian troops have entered from Somalia’s western border to fight al Shabaab militants. Ethiopian forces are now occupying several towns including Beledweyne, Somalia, that were formerly held by militants.

Wall Street Journal