The leader of the United Nations has called the coronavirus pandemic the most challenging crisis since the organization’s founding after World War II. But the Security Council, its most powerful arm, has been conspicuously silent.

Secretary General António Guterres has pleaded for a unified global response as many nations turn inward and seal each other off in an effort to contain the virus. He has also called for a halt to all armed conflicts so nations can focus on the crisis.

But without the supportive muscle of the 15-member Security Council, the only U.N. body empowered to authorize military and economic coercion to back its demands, Mr. Guterres’s calls have been widely disregarded. In Syria, Yemen, Libya, Afghanistan, Mali and Colombia, among other hot spots, fighting continues unabated. North Korea, which claims to have no coronavirus infections, launched two short-range missiles in recent days, its fourth weapons test in a month.

And there are few immediate indications that the situation will change, causing alarm and frustration among rights groups and foreign policy experts who say the United Nations is failing to fulfill its outsize role as the pandemic rages on across the globe.