WRAPUP 4-Sri Lankan troops move in on Tigers, 62,000 flee

* At least 62,000 flee, military says

* Tigers vow no surrender

* Tiger leader in war zone - Tigers

* Red Cross warns of catastrophe

(Updates number fleeing)

By C. Bryson Hull and Ranga Sirilal

COLOMBO, April 21 (Reuters) - Sri Lankan soldiers battled into the last redoubt of the Tamil Tigers on Tuesday, and an exodus of people trapped by the rebels in the coastal strip hit more than 62,000, the military said.

The International Committee of the Red Cross (ICRC) warned the situation was "nothing short of catastrophic" and urged both sides to prevent further mass casualties among civilians, saying hundreds had been killed in the past 48 hours.

The neutral agency did not assign blame to either side.