Al Jazeera’s Al Jazeera correspondent speaks to one of the victims of the US missile strike on Syria

An international human rights organisation has called on the United States to take immediate steps to protect civilians in Syria from a deadly US missile attack, calling it a “war crime”.

In a letter sent to President Donald Trump, the International Committee of the Red Cross (ICRC) said it was “deeply concerned” by the US attack on Syria, which it said killed at least 50 civilians including children.

The ICRC said in the letter that the “apparent targeting of civilians in densely populated areas, including residential areas, by the attack” by a US warplane on a Syrian military base on Wednesday, which also injured five civilians, was a “violation of international humanitarian law”.

The ICCR said the US strike on a “military target” in the vicinity of Damascus was a war crime and called for an immediate investigation into the incident.

The UN says at least 60,000 people have been killed in the Syrian conflict, which began in March 2011 with anti-government protests against the Assad government and has now killed over 250,000.

The US, which has been criticised for its use of chemical weapons in Syria, says its strike was in response to a chemical attack allegedly carried out by the Syrian government in March 2017 on the town of Khan Sheikhoun, near the Turkish border.

“The ICRC calls on the President to immediately halt the use of force against civilians, including children, in the context of a potential chemical attack in Syria,” said Ibrahim Hooper, a senior adviser at the ICRC’s regional office.

“We strongly condemn the US use of cruise missiles and other weaponry against innocent civilians in response in a way that is contrary to international humanitarian norms.”‘

War crimes’ The ICR said that the US raid on the Shayrat Airbase in the country’s north-east had been the first such attack by the United Nations-led coalition in Syria since it started bombing the government forces in the city in 2014.

The attack took place on the same day that the ICCR released its first report on the Syrian civil war, which found widespread violations of international law by the government of President Bashar al-Assad.

The report found that in addition to the Syrian army, other armed groups, armed paramilitary groups and terrorist groups were involved in the conflict, including the Islamic State (IS, formerly ISIS/ISIL) and al-Qaeda linked Jabhat al-Nusra.

The Syrian Observatory for Human Rights said at least 25 civilians, at least 15 children, had been killed and another 15 wounded in the strike.

A senior US official told Al Jazeera that the attack had targeted a convoy transporting military supplies to rebel-held areas of Syria and had targeted military equipment belonging to a local army unit.

US Defense Secretary Jim Mattis said the Pentagon had “absolutely no intention” of changing the military strategy of the Syrian military.

He said he did not believe the strike would change the military situation in Syria.

He also said he was not aware of any civilians being killed or injured in the attack.

He told reporters in Washington on Friday that the United states was “not going to change the course of action” of the war, saying the US military would “continue to act in the most robust way to support the Syrians, the rebels, to stop the use and proliferation of weapons of mass destruction”.

Mattis, who was visiting Washington, did not elaborate on the nature of the weapons and said the Syrian opposition had a responsibility to stop weapons of the regime.

The United Nations says at the time of the attack on the base, the US-led international coalition was conducting airstrikes against the Syrian regime of President Assad.

US Secretary of State Rex Tillerson said the White House was “concerned” by “the horrific actions that have taken place” in Syria and called on Russia to stop supporting the Syrian armed opposition.

He called on Moscow to ensure its “strongest possible” support for the Syrian people.

“It is critical that Russia, and other countries, act to prevent the Syrian rebels from further destabilising their country and the region,” Tillerson said.

Russia has consistently denied arming or providing arms to the rebel groups fighting the Assad regime.