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ASMARA, Eritrea (CNN) -- Ethiopia and Eritrea, blaming each other for their border war, gave uncompromising responses Thursday to an appeal by the U.N. Security Council for an end to fighting.

Meanwhile, a U.N. envoy warned that the heavily armed countries might ignite "the first high-tech war in Africa."

"The (U.N.) Security Council should point the finger at the culprits," Eritrean presidential adviser Yermane Gebremeskel said. "The Ethiopians initiated hostilities when we were both asked to show restraint."

Ethiopia's response to the council's demand for a cease-fire and immediate talks was equally uncompromising.

"This (U.N. call) would be better directed at Eritrea," Ethiopian government spokeswoman Selome Taddesse said in Addis Ababa. "We have been invaded and stayed put for nine months. They cannot ask us not to defend our sovereignty."

Peace hopes fade

The border war erupted last May when Eritrea occupied the contested Badme region as well as another pocket of land along the frontier. Fighting died down in June but reignited on Saturday and has spread to two fronts.

U.N. envoy Mohamed Sahnoun said he was optimistic when he arrived in Ethiopia and Eritrea last week seeking a diplomatic solution to the dispute, which has claimed 1,000 lives.

Sahnoun spoke with his old friends, Eritrean President Isias Afwerki and Ethiopian Prime Minister Meles Zenawi, and decided the doomsayers were wrong.

"I thought the reaction was positive," the Algerian diplomat said Wednesday. "I believed that given the kind of leadership they had, they would be able to resolve these problems."

But after heavy fighting broke out Saturday, Sahnoun said he decided the pessimists were right.

Angry and frustrated at what he called "this nonsensical war," Sahnoun said he cannot understand how two countries that appear to have modern leadership and a commitment to build a democratic system were fighting again.

Massive military buildup

Sahnoun said the current conflict poses a greater danger, because both sides have beefed up their arsenals in recent months.

"The military buildup on both sides has reached such a proportion that ... we might be witnessing soon the first high-tech war in Africa," he warned.

Diplomatic efforts to resolve the dispute foundered after Eritrea refused to accept a peace plan drawn up by the Organization of African Unity, which called on it to withdraw from Badme before negotiations on sovereignty begin.

Eritrea says it wants clarification on two points in the plan, which has been accepted by Ethiopia and is supported by the United Nations.

Publicly, the two countries say they are fighting over rights to tracts of remote, mostly uninhabited land along their 620- mile border. But the conflict may be less about disputed borders than ideological differences, trade problems and personal rivalry.

After the U.N. Security Council heard from Sahnoun on Wednesday, it unanimously approved a resolution demanding an immediate end to the fighting and a halt to arms sales to both countries.

"The alternative is full-scale war with horrendous destruction and repercussions in the region," Sahnoun warned.

He said the 15 nations on the council should now individually deliver the same strong message to Ethiopia and Eritrea: The fighting must end, or sanctions may be imposed.

The Associated Press and Reuters contributed to this report.

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