Saudi warplanes carried out an airstrike against the vital Yemeni aid port of Hodeidah on Sunday, hitting a radio station and killing four people. According to the Houthi movement, the slain were employees at the station.

Saudi officials have been escalating airstrikes against Hodeidah in recent days, but they declined comment to the press on why a radio station was attacked. Previous airstrikes have hit the fishing port and a bus depot in the city.

Hodeidah is the main aid port in Yemen, and is estimated to supply 70% of the nation’s food. It is the only port under Houthi control, and subsequently the lone source of aid for the entire north of the country. Its accessibility is in doubt, with Saudi-backed forces having seized the roads on the outskirts.

The UN has been trying to prevent the fighting from reaching the city itself, where hundreds of thousands in the city could be in mortal danger, and millions of lives could hang in the balance across Yemen. So far, efforts to get peace talks going have failed.