UNITED NATIONS - The U.N. Security Council has condemned "in strongest terms" Thursday's attack against a U.N. mission in the Democratic Republic of the Congo, in which at least 14 Tanzanian peacekeepers and five Congolese soldiers died.

Security Council members met in a closed session Friday afternoon to discuss the attack, after holding a moment of silence in tribute to the victims.

In addition to the deaths, 44 people were injured in the attack in DRC's North Kivu province, where a Ugandan rebel group known as the Allied Democratic Forces, or ADF, is active.

A U.N. official told VOA that the group was suspected to be behind Thursday's attack.

In its statement Friday, the Security Council said it expressed deepest condolences to the families of the victims, the governments of Tanzania and Democratic Republic of the Congo, and to the U.N. mission in DRC, known as MONUSCO.

Noting that this attack was the worst on U.N. peacekeepers in recent years, the statement said incident was a "reminder of the extraordinary sacrifices made by these brave women and men every day."

U.N. flags are expected to fly at half-staff on Monday, in tribute to the victims.

The U.N. mission said at least five Congolese soldiers were also killed in the protracted fighting between suspected ADF elements and MONUSCO and Congolese forces.

Tanzanian President John Magufuli has expressed shock over the attack. He addressed his constituents Friday, the day the attack was reported by the United Nations — and the day before Tanzania celebrates its independence day.

The U.S. State Department said it was "horrified" by the attack, in a statement from the department's Bureau of African Affairs. The statement extended "deepest condolences" to the peacekeeping mission, the Congolese military and the families of those killed.

FILE - U.N. Secretary-General Antonio Guterres spe FILE - U.N. Secretary-General Antonio Guterres speaks during a press conference in Nairobi, Kenya, March 8, 2017. FILE - U.N. Secretary-General Antonio Guterres speaks during a press conference in Nairobi, Kenya, March 8, 2017.

U.N. Secretary-General Antonio Guterres expressed his "outrage" after Thursday's attack, which also left about 44 people injured.

"I condemn this attack unequivocally," Guterres said Friday. "These deliberate attacks against U.N. peacekeepers are unacceptable and constitute a war crime."

"This is the worst attack on peacekeepers in the organization's recent history," he added.

Guterres said military reinforcements had arrived on the scene. "The force commander is there as well, coordinating the mission's response, and the medical evacuation of casualties is ongoing," he said.

"Attacks against those who are working in the service of peace and stability in the Democratic Republic of the Congo are cowardly and constitute serious violations," said MONUSCO chief Maman Sidikou in a statement. "MONUSCO will take all actions to ensure that the perpetrators are held accountable and brought to justice."