LONDON--Allied bombers heralding the final assault in Tunisia have set the Bizerte airport ablaze, a communique announced tonight, and other advices said Allied assault troops have sliced through to the sea between Tunis and Bizerte to pen up the Axis garrisons in the two ancient citadels.

Dispateches from Allied field headquarters said the battle for the spring-board to Europe had reached the "critical stage."

The communique reported that six more Axis planes and five American craft have been shot down in new air battles over the front but three of the American pilots were saved.

A previous communique said the fighting had progressed to cast of Djedeida, within ten miles of Tunis, but tonight's did not mention the exact positions, reporting that Allied advance units were keeping up strong pressure in the vicinity of Djedeida and Mateur, 20 miles south of Tunis