SANA, Yemen — An airstrike apparently carried out by the Saudi-led military coalition set off a huge explosion on Monday morning in Sana, the capital of Yemen, flattening homes close to the site and shaking buildings as far away as the outskirts of the city. At least 25 people were killed, according to witnesses and medical officials.

The explosion occurred around 10:30 a.m. in the Faj Attan area of the city, near a mountaintop air defense base that warplanes had been bombing for days. Residents speculated that a bomb had struck an underground munitions depot, which might have explained why the blast seemed like an earthquake at first, before erupting into a fireball seen for miles around.

Sana has been bombed almost daily for more than three weeks. The city has been a stronghold of the Houthi militia since September and a primary target for the Saudi-led aerial offensive, which is meant to cripple the Houthis and restore the exiled Yemeni government to power.