European Union aid is being risked by Ethiopia's continued opposition to the demarcation of its border with Eritrea.
There are fears the war could reignite
EU development programme head Richelle Koos said Ethiopia's rejection of the world court ruling means it might "lose its development partners".
Mr Koos said the issue is raised at every meeting with Ethiopian officials.
Tensions between the two countries have been high since Ethiopia rejected the ruling, which gave the symbolic town of Badme to Eritrea.
The EU is sending a high-level mission to Addis Ababa and Asmara in January, to try to end the border stalemate.
The two countries fought a two-and-a-half year border war, before signing a ceasefire in December 2000.
"If Ethiopia wants to keep its developing partners, it should be operating very carefully and listening to the position that have been taken," he told the Reporter newspaper.
"We have been consistent and firm in our opinion, and that means that every time we meet Ethiopian officials we will put this on the agenda and push for it," he said.
Ethiopia avoided the worst affects of a drought in the past year, in part because of a good response from donors to aid appeals.