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ASMARA, Eritrea (CNN) -- A three-day lull in fighting between Eritrea and Ethiopia ended Sunday when Ethiopian jets bombed sites near the Eritrean port of Assab, according to news reports and government officials.

The Eritrean military shot down an Ethiopian MI24 helicopter gunship on the Assab front early Sunday after Ethiopia launched an offensive on a new front southwest of the strategic Red Sea port of Assab, Eritrean officials said.

The attack had started with a massive Ethiopian bombardment by artillery and an Antonov aircraft, an Eritrean government spokesman said.

"Such an attack is normally the prelude for an infantry attack," Yermane Gebremeskel, a spokesman for the Eritrean president, told Reuters.

There was no immediate comment from the Ethiopian government. Fighting between Ethiopia and Eritrea over their disputed border restarted on February 6 on the Badme and Zalambessa fronts but the fighting had eased on Wednesday.

Reports of casualties were not yet available.

Signs of the escalating dispute were evident, as troops on Sunday massed on both sides of Bure along the border 70 kilometers (45 miles) southwest of Assab, the easternmost front along the two countries' 1,000-kilometer (600-mile) stretch of border.

The Eritrean government ordered the residents of Zalambessa, another front line border town 100 kilometers (60 miles) south of Asmara, to evacuate.

Although the port itself and the town of Assad escaped Sunday's bombardment, the attacks appeared to be a warning to Eritrea that Ethiopia may be willing to destroy the port, 580 kilometers (355 miles) southeast of Asmara, if the fighting continues to escalate.

The eastern Red Sea port was the key outlet for landlocked Ethiopian cargo before war first erupted last May.

The war has disrupted trade and traffic. Since it began, Ethiopia has halted all traffic through Assab and transferred its ships and deliveries to the port of Djibouti.

Eritrea lost millions of dollars in revenue when Ethiopia moved its business elsewhere.

The evacuated border town of Zalambessa has been a front since June, when Eritrean forces took control shortly after the start of fighting.

Ethiopian shelling has continued since then, but residents packing up Saturday said the artillery attacks had become far more frequent in the past week, forcing townspeople last week to spend full days inside underground bunkers.

On Saturday, Zalambessa was nearly a ghost town, with just a handful of residents still preparing their departure.

More than 1,000 people were killed by air bombardments, shelling and border fire in the first weeks of the war in May and June, 1998.

Hostilities waned in June, when a U.S.-brokered moratorium on air strikes was adopted, and tensions simmered over the next eight months as troops massed along the border and sporadically exchanged artillery fire.

But full-scale fighting erupted again, and Ethiopia last week repeatedly used jet bombers in violation of the moratorium, inviting Eritrea's condemnation.

Each side has since claimed victory in battles on several fronts, but while Ethiopia has refused to give reporters access to conflict regions to verify any of its claims, Eritrea has allowed journalists to visit front lines and speak with soldiers and prisoners.

The Associated Press and Reuters contributed to this report.

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