U.N. Secretary-General Ban Ki-moon on Monday welcomed the escape of some 30,000 civilians from the so-called no-fire zone in northern Sri Lanka, where military forces are battling Tamil Tiger militants. Sri Lankan troops broke through a defensive earthwork used by the Tamil Tigers, opening a breach that the government said allowed 30,000 civilians to escape. An estimated 150,000 civilians were believed to be trapped between the two sides before Monday's breach. “While the departure of civilians to safer areas is welcome news, he remains deeply concerned about the circumstances of the civilians that remain in the conflict zone and the potential for large-scale casualties,” Ban's office said in a statement. “He deplores the continued use of heavy weapons in the vicinity of civilians, and the use of force by the Liberation Tigers of Tamil Eelam (LTTE) in preventing the departure of civilians from the conflict zone,” the statement said. As the civilians were fleeing, three Tamil Tiger suicide bombers detonated explosive vests killings dozens of civilians, Sri Lanka's government said. “The secretary general stresses that it is now imperative for U.N. staff to be allowed into the conflict zone to facilitate relief operations and the evacuation of civilians. Humanitarian agencies must be allowed to assess needs and bring in adequate relief supplies,” the statement added.