During a night attack on Tuesday, Jeep-loads of Eritreans rushed into the desert to find large bomb craters near Assab's underground reservoir. Still burning, the powerful incendiary bombs have so far missed the pump house.
There is an atmosphere of siege. With the port, the oil refinery and all overland trade at a standstill, Assab is the most isolated - and strategically important - target in the war in the Horn of Africa between Ethiopia and Eritrea.
"I can put on my radio and know what is going on in the rest of the world, but I have no idea what is happening in Eritrea," one resident said.
Until it was connected to a satellite link this week, Assab had been without telecommunications for eight months after Ethiopia cut off the telephones. "You can call it a state of emergency," said Abdulla Aden, a senior official from the governor's office.
The isolation is heightened by the growing anxiety in Eritrea that the international community wants to appease Ethiopia, the Goliath of this war. Diplomats informally acknowledge this. "Ethiopia is a large, regionally important country, which we don't want to see fragment or weaken," one diplomat said.
This week the conflict took a new twist when Assab became the target of Ethiopia fighter jets and Antonov planes, which fly high over the front-line defence about 70km west of the city. The port remains untouched, heavily defended by anti-aircraft guns and tanks.
An Ethiopian helicopter shot down last Sunday lies near the trenches that weave along the desert ridge at the border. The pilot's charred body remains in the wreckage; the other crew members have been incinerated. They do not deserve burial, says Colonel Alem Seged, who strides behind the lines holding a pistol, binoculars and a leather briefcase. "They were trying to kill us, so why should we do that for them?"
The battle for Assab has changed the nature of the conflict. Ostensibly it began as a border skirmish, but the Eritreans are now convinced that land-locked Ethiopia wants to seize its main port. "First it was Badme, but now Ethiopia wants to annex the port," says Tesfu Tewolde, vice-chairman of Eritrean Shipping Lines. He says he is waiting for peace for business to start up again.
Assab, once a major transit station for cargo ships calling at the Red Sea ports in Yemen and Dubai, has been reduced to servicing only four ships a month. More than 90 per cent of its business was lost when Ethiopia boycotted the port over a currency and access issue last March, and started using neighbouring Djibouti instead.
About 20,000 Ethiopian workers left, bars closed, and the machinery at the dock stands idle. A once cosmopolitan trucking town has become a military city. Land cruisers camouflaged with tar and mud race the empty streets, and soldiers in fatigues fill the pavements. Hungry for custom, supermarkets depend on supplying the military with pasta, tinned fish, tomato paste and jam.
The city's remaining Ethiopians run some of the surviving businesses, but tension over the recent battles has made them fearful. The military seized about 10 Ethiopian businessmen after the bombing raids started this week. "They think some of us are informers," one Ethiopian man said.
It is a curious feature of this war that Ethiopians have generally been allowed to continue a normal life in Eritrea, while Ethiopia has deported 52,000 Eritreans. Most were driven to the border and made to walk with their few possessions across the no-man's land between the two countries. Idle cargo ships in Assab were turned into passenger vessels, shipping 1,500 at a time to ports in Masawa, further north.
In December and January alone, more than 25,000 deportees passed through Assab, many of whom had been born in Ethiopia.