NAIROBI, Kenya — A bridge that’s crucial to delivering desperately needed food to much of Ethiopia’s Tigray region has been destroyed, an aid group said Thursday, as Tigray fighters were said to be approaching other combatants occupying large areas nearby.

The destruction of the bridge over the Tekeze River “means aid efforts will be even more severely hampered than before,“ the International Rescue Committee said in a statement.

It was not immediately clear who destroyed the bridge on a main supply route linking western Tigray, which is occupied by forces from the neighboring Amhara region, and the rest of Tigray.

The Tigray forces, emboldened after retaking the regional capital this week in a stunning turn in the eight-month war with Ethiopia’s military, have taken control of key towns this week, and several thousand fighters had been seen to be moving west.

The spokesman for the Tigray forces this week told The Associated Press they would “liberate” the region from “enemies” including the Ethiopian forces, Amhara forces and soldiers from neighboring Eritrea.

Ethiopia’s government, under pressure from battlefield losses amid some of the fiercest fighting of the war, this week declared an immediate and unilateral cease-fire. While witnesses have seen Eritrean forces retreating toward the border Eritrea shares with Tigray, Amhara authorities have warned the Tigray forces against trying to retake western areas.

As Tigray faces the worst famine crisis in a decade, humanitarian aid groups are still badly constrained, with electricity and communications links still cut in the Tigray region and main supply routes blocked.

In one case, a 29-truck convoy carrying World Food Program aid was denied access and had to return to the Amhara region earlier this week, a U.N. humanitarian worker said. The worker spoke on condition of anonymity for fear of retribution.