CAIRO — Aid workers in Yemen gained entry on Tuesday to a major food storage warehouse where grain has languished for nearly six months because combat had made it inaccessible, a break that offered some hope in the country’s worsening humanitarian crisis.

Access to the warehouse, the Red Sea Mills near the port of Hudaydah, where 51,000 tons of grain had been stranded since September, came as the United Nations appealed for $4 billion from international donors to save millions in Yemen from starvation.

Officials with the World Food Program, the United Nations anti-hunger agency, crossed the front line to enter the Red Sea Mills and inspect the grain, finding it largely intact. The mission eased fears that the stockpile, which could feed 3.7 million people for a month, could spoil and go to waste.

The Red Sea Mills had come to symbolize how armed conflict and starvation are deeply intertwined in Yemen, where relief aid is routinely manipulated by the belligerents as a tool of negotiation or a weapon of war.