Sudan on Saturday accused Ethiopia of an "unforgivable insult" in its sharpest statement since a decades-old border dispute flared late last year.
Clashes erupted between Sudanese and Ethiopian forces over Al-Fashqa, an area of fertile land settled by Ethiopian farmers that Sudan says lies on its side of a border demarcated at the start of the 20th century, which Ethiopia rejects.
In a statement on Thursday, Ethiopia's foreign ministry said it believes "the conflict being trumpeted by the Sudanese government's military wing could only serve the interests of a third party at the expense of the Sudanese people."
Sudan's foreign ministry responded on Saturday by saying "slander towards Sudan and accusation of being an agent for other parties is a grave and unforgivable insult."
It added: "What the Ethiopian foreign ministry cannot deny is the third party whose troops entered with Ethiopian troops trespassing on Sudanese land."
Earlier this week, Sudan accused Ethiopian troops of crossing the border after a similar act by Ethiopian aircraft last month, both of which Ethiopia denied.
Ethiopia on Thursday reiterated its accusation that Sudan had invaded in early November, attacked and displaced Ethiopians and took control of vacated military camps.
In its statement, Sudan said that Ethiopia had affirmed the 1903 border agreement several times, most recently in 2013.
It accused Ethiopia's foreign ministry of "exploiting (the border issue) for personal interests and for the specific interests of a certain group."
Both countries called on each other to pursue legal means to resolve the border issues.
An African Union mediator arrived in Khartoum on Thursday to discuss the conflict, as well as the ongoing negotiations between Sudan, Egypt, and Ethiopia over the Grand Ethiopian Renaissance Dam.
Ethiopian foreign ministry official spokesman Dina Mufti, state minister of foreign affairs Redwan Hussein and Prime Minister Abiy Ahmed's spokeswoman Billene Seyoum did not immediately respond to requests for comment on Saturday.