By Angela Dewan and Joshua Berlinger

WASHINGTON — (CNN) The Syrian army denied Tuesday that it was responsible for an attack on an aid convoy and warehouse that killed around 20 people near Aleppo.

“There is no truth to reports circulated by some media outlets that (the) Syrian army targeted the humanitarian aid convoy in rural Aleppo (governorate),” the state-run Syrian Arab News Agency reported, quoting a military source.

The United Nations and aid agencies say a 31-truck convoy and a warehouse storing aid was struck Monday night.

[Breaking news update 08:32 a.m. ET]

Russian or Syrian aircraft did not carry out airstrikes against a UN humanitarian aid convoy near the city of Aleppo, Russian Defense Ministry spokesman Igor Konashenkov said Tuesday in a statement on Facebook.

The ministry said it had “closely studied” video from the apparent scene of the attack taken by “so-called activists” and said it saw no evidence that the aid convoy was hit by an ammunition strike.

The United Nations and aid agencies said their 31-truck convoy was attacked on Monday night but has not said whether it was hit by an airstrike or shelling, or in any other way.

[Previous story published 8:28 a.m. ET]

The United Nations is suspending its aid operations in Syria after a deadly attack Monday night on a convoy carrying life-saving supplies for 78,000 people west of Aleppo, a UN spokesman said.

No one has claimed responsibility for the attacks, and it is unclear whether an airstrike hit the convoy or it was shelled.

The suspension was “an immediate security measure” and “we are committed to stay and deliver to everybody in need in Syria” in the longer term, Jens Laerke, a spokesman for the UN Office for the Coordination of Humanitarian Affairs, told a news conference in Geneva, Switzerland.

Laerke said the attack marked a “very, very dark day for humanitarians in Syria,” joining aid organizations such as the International Committee of the Red Cross and the World Food Programme in condemning it.

The ICRC said around 20 civilians were killed as well as a staff member of the Syrian Arab Red Crescent in the strike on the convoy, which hit 18 of the 31 trucks as well as the warehouse.

The attack came just hours after Syrian authorities declared an end to a fragile ceasefire in the war-torn country. The ceasefire had been called specifically to allow aid into some of the most desperate parts of Syria.

While some aid was delivered, agencies were severely hampered in the initial days of the ceasefire, unable to cross the border into Syria as they lacked permits from the government, UN officials said last week.

The convoy, however, had come from inside Syria, the World Food Programme told CNN. It was carrying crucial aid to around 78,000 people when it and the aid warehouse were attacked near the embattled city of Aleppo, the United Nations and aid agencies said. The area west of the city is reportedly rebel held.

UN and US officials said they were “disgusted” and “outraged” by the attack.

Red Crescent warehouse ablaze

Syrian Civil Defense, a volunteer emergency medical service, posted video of the attack’s aftermath on social media showing a warehouse ablaze and claiming that helicopters had dropped four barrel bombs on the site of a Syrian Arab Red Crescent aid warehouse, blaming the Syrian regime.

CNN cannot confirm the authenticity of the video or who was responsible for the attack.

Omar Barakat — the Syrian Arab Red Crescent’s director in Urum al-Kubra — was the staff member killed at the warehouse, ICRC Middle East public relations officer Krista Armstrong told CNN.

ICRC also said it was suspending its operations in Aleppo for three days.

“From what we know of yesterday’s attack, there has been a flagrant violation of international humanitarian law, which is totally unacceptable,” ICRC President Peter Maurer said in a statement.

“Failing to respect and protect humanitarian workers and structures might have serious repercussions on ongoing humanitarian operations in the country, hence depriving millions of people from aid essential to their survival.”

At least 32 people were killed in separate attacks Monday in Aleppo and its western suburbs, according to the UK-based Syrian Observatory for Human Rights.

Russia, US trade barbs

Russia and the United States were quick to blame each other for contributing to the latest deadly violence.

The US State Department said: “The destination of this convoy was known to the Syrian regime and the Russian Federation and yet these aid workers were killed in their attempt to provide relief to the Syrian people.”

Kremlin spokesman Dmitry Peskov said: “Unfortunately we’re sad to state that for this time — and it’s been over a week now — our American colleagues failed to separate rebels from so-called moderate opposition.”

The United States has supported and armed what it considers moderate rebels in Syria fighting militants groups such as ISIS, while Russia has supported the Syrian regime and considers all rebel groups “terrorists.”

Before news of the convoy attack broke, neither the United States nor Russia — which brokered the pact — publicly declared the ceasefire over, causing some confusion over whether it was still in place.

The State Department also blamed Moscow and the Syrian regime for hampering the delivery of aid.

“For more than a week, we have urged Moscow to fulfill the commitments it made in Geneva to facilitate the unimpeded flow of humanitarian aid to the Syrian people,” the department said in a statement.

“And for more than a week, the Syrian regime repeatedly denied entry to these UN convoys, preventing them from delivering urgent food, water and medical supplies to desperate Syrian citizens.”

Eastern Aleppo desperate

Getting aid to areas cut off by fighting has been a growing concern for humanitarian agencies — with trucks destined for eastern Aleppo, where an estimated 250,000 civilians have been short of food, medicine and water. The area was essentially cut off in July when the Syrian government launched a siege and encircled the rebel-held area.

“Our outrage at this attack is enormous,” said Staffan de Mistura, the UN special envoy for Syria. “The convoy was the outcome of long process of permission and preparations to assist isolated civilians.”

Stephen O’Brien, the head of the UN’s relief organization, said he was “disgusted” by the reports and that the strike would amount to a war crime if it’s discovered that aid workers were deliberately targeted.

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