The commander of the 3,500-plus European Union force to be deployed to Chad and Central African Republic in coming weeks said his troops would fire back if attacked by Chad rebels, but emphasised they would not interfere in local power struggles.

Irish Lieutenant-General Patrick Nash said the EU force would be fully operational by mid-May and would aim to have created a safe and secure environment in the regions bordering Darfur within an initial 12-month mandate.

"Progress will have been made in allowing the beginnings of the IDPs (internally displaced persons) to return," Nash told a news conference of the mission's core aim to protect civilians and aid workers caught up in violence spilling over from Darfur.

However Torben Brylle, EU special representative for Sudan, voiced concerns about the impact of expected delays to the much larger joint U.N.-African Union force in Darfur after the United Nations forecast that it would take most of 2008 to deploy.

"We see with concern the delays and difficulties in terms of UNAMID," he said of the force. "We believe there could be positive synergies from the simultaneous deployment of the two operations... It is regrettable."

The head of U.N. peacekeeping, Jean-Marie Guehenno, said on Monday full deployment of the 26,000-strong U.N.-AU force would be delayed because of conditions set by the Sudanese government, including the rejection of some non-African contingents.

The Darfur conflict in western Sudan has taken some 200,000 lives and driven more than two million from their homes since rebels took up arms against the government in 2003.

In what is likely to be the EU's most challenging security mission to date, foreign ministers of the 27-member bloc agreed on Monday to launch the Chad mission after months of delays caused by shortages of key equipment such as helicopters.

Former colonial power France is expected to provide more than half the troops but Nash stressed that more than a dozen other nations would be present, and that it would be completely separate from a French force already on the ground.

Asked if EU forces would fire back if shot on by Chad rebels, he replied "yes", but rejected rebel suspicions that the force would favour Chad leader Idriss Deby.

"We have a clear mission. If the rebels are not interfering in our mission, it is no business of ours," he said of tasks including patrols, quick-reaction interventions and special operations.

Nash noted that while EU nations had contributed enough equipment and troops to launch the force, he would still need extra air transport and ground troops to achieve a full deployment of some 3,700 through the life of the mission.