Hiruy denies being an Ethiopian stooge
An alliance of 13 Eritrean opposition groups says it is setting up a military wing to topple President Isaias Afewerki.
The Eritrean National Alliance's general secretary, Hiruy Tedla Bairu, told the BBC that the military wing would attack strategic targets such as television and radio centres.
Mr Hiruy said the military wing would not attack the Eritrean army, which he hoped could be won over by the opposition.
Meanwhile, the Eritrean Islamic Jihad Movement has denied allegations that it was responsible for last month's murder of a British geologist.
We wish to get rid of the dictatorship in our country and the natural thing to do is to ally ourselves with our immediate neighbours
Mr Hiruy also said that the alliance would not seek to target President Isaias because "the problems [assassinations] produce later are too big to handle".
He was speaking in neighbouring Ethiopia, which he said was one of three countries that had offered his alliance "material support".
He said the others were Sudan and Yemen but denied that the ENA were Ethiopian stooges.
"We wish to get rid of the dictatorship in our country and the natural thing to do is to ally ourselves with our immediate neighbours," Mr Hiruy said.
Ethiopia and Eritrea fought a bitter two-year border war, which ended in 2000.
The Eritrean Islamic Jihad Movement said that it did not kill UK geologist Timothy Nutt and that its policy was only to attack government targets in Eritrea.
Mr Nutt was found in a ravine near the town of Bisha, with his throat cut and his four-wheel-drive car burn out nearby.
He worked for the Canadian-based Nevsun Resources, which is prospecting for gold and diamonds.
The Eritrean Government blamed the murder on the Islamic Jihad militants who, it says, are backed by Sudan and are seeking to deter foreign investment in Eritrea.