"I intend to immediately despatch a UN humanitiarian team to the no-fire zone," he told reporters in Brussels, after a Somalia donors conference.
"The purpose of this humanitarian team will be to first of all monitor the situation and support the humanitarian assistance and try to do whatever we can to protect the civilian population," the UN chief said.
"It is critical that this team be allowed into the no-fire zone as soon as possible, and I'm asking for the strong support and speedy assistance of the Sri Lankan government."
According to the Sri Lankan military, Tamil Tiger (LTTE) rebels were encircled Thursday in a tiny strip of land by government troops but were still putting up stiff resistance despite calls to surrender.
The army said the guerrillas controlled a mere 10-12 square kilometres (around four square miles) of territory on the northeast coast, where thousands of civilians are still trapped by the fighting.
"I am most concerned at the rapidly deteriorating