The Pentagon has confirmed that the preparing was intended for an evacuation of the U.S. Embassy in Sudan.

It would not be easy to get embassy staff out, some U.S. officials acknowledged, let alone the estimated 19,000 American citizens believed to be in Sudan.

The U.S. is moving more troops to Djibouti, where it has a base. The moves came as fighting intensified yesterday in Sudan; a bombardment by warplanes in the center of Khartoum, the capital, was one of the most fearsome assaults yet.

But Sudan’s airspace is closed.

The international airport in Khartoum has been the target of heavy shelling, leaving destroyed planes littering the tarmac.

A State Department spokesman said that, because of fighting there, an evacuation is not currently safe.

The death toll rose to 330, with nearly 3,200 others wounded, according to the W.H.O.

The clashes between two generals have upended a transition to a civilian-led democracy.

Meanwhile, the U.N. secretary general, António Guterres, called for a three-day cease-fire to commemorate the holiday of Eid al-Fitr, but past cease-fires have not held.