"It's a groundless accusation, a total fabrication," said Yemane Gebremeskel, director of Eritrean President Isaias Afwerki's office.

The denial followed reports in the Sudanese media quoting Faruq Hassan Mohamed, the governor of Sudan's eastern state of Kassala, as saying Eritrea was boosting its forces along the border for the purposes of spying.

Faruq was quoted as saying that Eritrea is "carrying out surveillance activities in conjunction with some armed groups" and that officials in Kassala were "conducting an extensive security operation in anticipation of aggression".

Gebremeskel dismissed the allegations, saying Faruq had "made a habit" of making such charges.

Relations between Eritrea and Sudan are tense with the two governments frequently accusing each other of supporting opposition movements on the other's soil.