Although analysts initially estimated the T.P.L.F. had 250,000 men under arms, it quickly became clear that its force was much smaller. Government soldiers and allied ethnic militias surrounded the T.P.L.F.’s forces by sealing Ethiopia’s borders with Eritrea and Sudan, effectively severing the rebels’ supply lines.
And the T.P.L.F. received an unexpected blow when soldiers from Eritrea, Ethiopia’s former enemy, crossed into Tigray to fight alongside Mr. Abiy’s forces. In such conditions, experts say, it’s unclear how long the T.P.L.F. can hold out.
Still, the situation is fluid and unpredictable. Border clashes between Ethiopia and Sudan in recent weeks, over a patch of disputed farmland, could play to the advantage of the T.P.LF. if Sudan helps the rebels to resupply.
And the top military commanders of the T.P.L.F. remain at large. Two Western officials and one with the T.P.L.F., who were not authorized to speak publicly, identified Lt. Gen. Tsadkan Gebretensae, a former head of the Ethiopian military, as a senior rebel leader.
General Tsadkan led Ethiopia into combat against Eritrea during the two countries’ brutal border war between 1998 and 2000. In recent years, after retiring from the army, he ran a small brewery. Now 66, he is back in the fight with the newly formed Tigray Defense Forces, battling the Ethiopian army he once commanded.
One T.P.L.F. stronghold, the Western officials said, is in the Tembien mountains, a cluster of jagged hills and narrow winding roads in central Tigray — part of a highland massif often called the “rooftop of Africa.”
Kjetil Tronvoll, an expert on the T.P.L.F. at Bjorknes University College in Oslo, said the party’s leadership has likely dispersed in small groups, to spread the risk of capture.