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MOGADISHU, Somalia — A huge truck bomb blast in Somalia's capital has killed 276 people and wounded roughly 300 more, the country's information minister said Sunday.

It is believed to be the single deadliest attack ever in the Horn of Africa nation.

Doctors struggled to assist horrifically wounded victims, many burned beyond recognition. Officials feared that the toll would continue to climb from Saturday's truck bomb, which targeted a busy street near key ministries.

A man runs from a massive explosion Sunday in front of the Safari Hotel in Mogadishu, Somalia. SAID YUSUF WARSAME / EPA

Ambulance sirens still echoed across the city as bewildered families wandered in the rubble of buildings, looking for missing relatives. "In our 10 year experience as the first responder in #Mogadishu, we haven't seen anything like this," the Aamin Ambulance service tweeted.

Grief overwhelmed many. "There's nothing I can say. We have lost everything," said Zainab Sharif, the mother of four children, who lost her husband. She sat outside a hospital where he was pronounced dead after hours of efforts by doctors to save him from an arterial injury.

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President Mohamed Abdullahi Mohamed declared three days of mourning and joined thousands of people who responded to a desperate plea by hospitals to donate blood.

Dr. Mohamed Yusuf, director of Medina hospital, said: "The hospital is overwhelmed by both dead and wounded. We also received people whose limbs were cut away by the bomb. This is really horrendous, unlike any other time in the past."

Photos from the scene. In our 10 year experience as the first responder in #Mogadishu, we haven't seen anything like this. pic.twitter.com/cNxeDD86u6 — Aamin Ambulance (@AaminAmbulance) October 15, 2017

Overnight, rescue workers with flashlights searched for survivors trapped under the rubble of the largely destroyed Safari Hotel, which is close to the Foreign Ministry. The explosion blew off metal gates and blast walls erected outside the hotel.

The government has blamed the al-Qaida-linked extremist group al-Shabab for the attack, which it called a "national disaster." However, al-Shabab, which often targets high-profile areas of the capital with bombings, had yet to comment.

Photos: Somalis Search for Survivors After Mogadishu Truck Bomb Blast

"They don't care about the lives of Somali people, mothers, fathers and children," Prime Minister Hassan Ali Khaire said. "They have targeted the most populated area in Mogadishu, killing only civilians."

Somali soldiers helps a wounded civilian from a truck blast Saturday in Mogadishu, Somalia. Farah Abdi Warsameh / AP

Information Minister Abdirahman Omar said the blast was the largest the city had ever seen. "It's a sad day. This is how merciless and brutal they are, and we have to unite against them," he said on state-run radio.

The United States joined the condemnation, saying: "Such cowardly attacks reinvigorate the commitment of the United States to assist our Somali and African Union partners to combat the scourge of terrorism."

The U.S. military has stepped up drone strikes and other efforts this year against al-Shabab, which is also fighting the Somali military and more than 20,000 African Union forces in the country.

Saturday's blast occurred two days after the head of U.S. Africa Command was in Mogadishu to meet with Somalia's president and two days after the country's defense minister and army chief resigned for undisclosed reasons.