NAIROBI - New satellite imagery of one of the world’s most reclusive nations shows a military buildup inside Eritrea near the border with Ethiopia’s northern Tigray region, backing up witness accounts of a new, large-scale offensive.

Eritrea has fought alongside Ethiopia against Tigray forces. Witnesses in Eritrea this month told The Associated Press that people including students and public servants are being rounded up across the nation and sent to fight in the new offensive.

The satellite imagery provided by Maxar Technologies shows what Maxar described as battle tanks, self-propelled howitzers and a M-46 field gun battery in the Eritrean town of Serha, near the border, on Sept. 19. The town is across the border from the Tigray town of Zalambessa, one of the first communities overrun in the war.

The U.S. envoy to the Horn of Africa, who has been pressing the Ethiopian and Tigray sides to stop fighting and hold peace talks, told reporters last week that Washington has been tracking Eritrean troop movements across the border.

“They are extremely concerning, and we condemn it,” Mike Hammer said. “All external foreign actors should respect Ethiopia’s territorial integrity and avoid fueling the conflict.”