European Union troops in eastern Chad stepped up patrols around refugee camps on Friday and aid workers restricted movements after anti-government rebels announced an offensive.
Chad's government and its rebel opponents have given sharply conflicting versions of reported military movements in the Dar Sila region near the Sudan border, where Irish EU soldiers are protecting U.N.-run camps for Sudanese and Chadian refugees.
The Irish are part of an EU military mission in Chad whose mandate is to protect civilians, including more than 200,000 Sudanese refuges who have fled the five-year-old conflict in Sudan's Darfur region, which lies on Chad's eastern frontier.
While Chadian rebel spokesmen said their fighters were advancing westwards in strength and had shot down a government helicopter, government officials rejected "rebel propaganda" and said the helicopter had crash-landed with "technical problems".
Nevertheless, an earlier statement by the government in N'Djamena said "mercenaries in the pay of Sudan" - the term it uses to describe rebels fighting to topple President Idriss Deby - had crossed into Chad over the eastern border on Wednesday.
At Goz-Beida, where U.N. agencies and humanitarian NGOs operate camps for the Sudanese and Chadian refugees, Irish troops of the 97th Infantry Battalion patrolled in and around the town on foot and in armoured vehicles.
"We are continuing to monitor the situation, patrol Goz-Beida and talk to the NGOs," said the battalion spokesman Commandant Stephen Morgan. The Irish in their green battledress were conspicuous in the lighter desert colours of the region.
The Irish battalion said on Thursday it had received reports of combat between rebel forces and government helicopters at Modeina, 70 km (40 miles) northeast of Goz-Beida.
A Reuters reporter in Goz-Beida said U.N. and aid agency vehicles stayed parked because relief workers restricted travel as a precaution due to fears of renewed conflict in the east, from where rebel columns have launched offensives in the past.
"Oxfam has stopped all circulation in the field as a precaution until further notice because the security situation is unclear," Aimee Nsari, programme manager at Goz-Beida for Oxfam Great Britain, told Reuters.
