Sri Lanka's rebels declared a unilateral cease-fire Sunday, but the government refused to halt its offensive into the last strip of land the insurgents hold despite concerns for tens of thousands of civilians trapped there. A top UN official urged Sri Lankan leaders to let aid into the tiny war zone along the northeastern coast, as reports have grown of starvation and casualties among those stuck inside. The rebels, who have voluntarily halted their fight before, said in a statement e-mailed to The Associated Press that the "humanitarian crisis can only be overcome by the declaration of an immediate cease-fire." They urged the international community to persuade the government to lay down its arms also. But Sri Lanka's Defense Secretary Gotabhaya Rajapaksa rejected the call saying the rebels were "running" from government forces. In recent months, troops have pushed deep into the Tamil Tigers' strongholds in the north, surrounding the beleaguered rebels and vowing to end the quarter-century war.