MOGADISHU, Somalia — When a double truck bombing shattered the night in Mogadishu on Saturday, rescue workers began the grim search for survivors that has become all too common as Somalia battles an Islamist insurgency. They picked through burned-out cars and hunted as best they could in a collapsed hotel.

But it was only on Sunday, as emergency workers pulled body after body from the rubble of a nearly leveled downtown street, that the magnitude of the latest attack came into focus. The numbers of dead surged from 20 on Saturday night to more than 270 and counting, according to government officials. More than 300 people were injured.

“This is the deadliest incident I ever remember” since the 1990s, when the government collapsed, a shaken Senator Abshir Ahmed said in a Facebook posting.

The attack came as the United States under President Trump has made a renewed push to defeat the Shabab, Somali-based militants who have terrorized the country and East Africa for years, killing civilians across borders, worsening famine and destabilizing a broad stretch of the region. While no one had yet claimed responsibility for the bombings, suspicion immediately fell on the group, which frequently targets the capital, Mogadishu.

The Shabab — which once controlled most of the city — have lost much of their territory in recent years, the result of attacks by African Union forces, a fitfully strengthening Somali Army and increasing American air power. But the group remains a potent killing force, despite years of American counterterrorism operations.

Some of the militants have proclaimed allegiance to Al Qaeda, while others support the Islamic State.