SAUDI ARABIA has charged that a missile launched from Yemen toward Riyadh's international airport on Saturday was supplied by Iran and assembled by Tehran's Lebanese client, Hezbollah. It says this could be considered "an act of war" and claims the right to "respond to Iran in the appropriate time and manner." Yet the only action taken so far by the de facto Saudi ruler, Mohammed bin Salman, has been to besiege some of the world's most desperate people — the cholera-stricken and literally famished civilian population of Yemen.

The press of multiple international crises and President Trump's monopolization of media attention have helped obscure the severity of the humanitarian emergency in Yemen, a poor country of 28 million that has been devastated by civil war and a Saudi-led military intervention. According to the United Nations, it is suffering the fastest-growing cholera epidemic ever recorded, with about 895,000 cases and nearly 2,200 deaths since April. At the same time, it is facing the world's biggest food emergency, with 7 million people requiring urgent assistance.

Children have been disproportionately afflicted. According to U.N. figures, 27 percent of the cholera victims are under the age of 5. Officials estimate that juvenile cholera cases will reach 600,000 by the end of the year. Meanwhile, hunger has left half of children under 5 stunted, and 2.2 million are affected by either moderate or severe malnutrition.

Saudi Arabia bears heavy responsibility for this suffering. For 2½ years, it has pursued a ruthless but unwinnable war against ethnic Houthis who have captured much of the country, including the capital, Sanaa, and the largest port, Hodeida. Bombing raids have repeatedly struck hospitals and food markets. Worse, in the name of preventing Iran from delivering weapons to the Houthis, the Saudis and their allies have blockaded the country by sea and air, closing Sanaa's airport to commercial traffic and slowing food imports at Hodeida.

Now, in reaction to the missile firing, the Saudis have announced a more thorough closure of "all Yemeni ground, air and sea ports." Though a government statement said it would take "into consideration the continuation of the entry and exit" of humanitarian supplies and aid workers, U.N. officials say that aid flights have been blocked. The World Food Program warned that hundreds of thousands of children would be "on the brink of starvation" if the blockade lasted even for two weeks.

Saudi officials say the siege is meant to prevent what they claim was the smuggling of missile parts into Yemen from Iran. It has offered no proof of the rocket's origin, and experts point out that Yemen is known to have imported Scud missiles from North Korea before the war. In any case, the blockade will not deter either Iran or the Houthis, but it could trigger a full-blown famine among innocent children. The Trump administration, which has blithely backed Crown Prince Salman in his reckless adventures, should consider the cost.