Chemical weapons attack latest in litany of Syria atrocities

With its missile strike on Shayrat air base in central Syria, Washington signaled that it had judged President Bashar Assad responsible for the horrific chemical weapons attack in northern Syria that drew international outrage last week. But it is not the first or even deadliest atrocity of the war.

Rights groups and many Middle Eastern and Western nations say Assad is responsible for a litany of war crimes in the six years he and his supporters have struggled to extinguish a popular uprising and armed insurgency against his rule.

The violence started early on, with detentions, torture, and summary executions, and escalated to bombardment, massacres, sieges, and chemical warfare. Various monitors put the war's toll at over 400,000 killed. The United Nations has recorded 5 million refugees from the conflict, and says about half the country's population is displaced within Syria's borders or abroad.

Assad has denied responsibility for all specific allegations of war crimes. He maintains his war is one against terror, though he acknowledges that civilians have sometimes been caught in the cross-fire.

Here are some of the 6-year-old war's worst atrocities:

Barrel bombs

Though not the deadliest weapon in the government's arsenal, the so-called barrel bomb is now synonymous with Syria's civil war. The crude, unguided munition — oil barrels packed with explosives and shrapnel — is emblematic of the government's determination to brutalize its opponents. Soldiers roll them off of helicopters above opposition areas to slam into markets, hospital, schools and military baes below.

Sometimes squadrons will bomb an area twice, minutes apart, to kill the first responders who have gathered in the area — a grisly scenario dubbed a "double tap" attack. Thousands of people have been killed in documented barrel bomb attacks, though Assad denies they even exist.

Bayda and Baniyas massacres

On May 2 and 3, 2013, government troops and government-backed militias stormed the towns of Bayda and Baniyas on Syria's coast and, according to a Human Rights Watch investigation, went door to door burning homes and shooting families in cold blood. At least 248 people were killed. The troops were allegedly looking for army defectors and other dissidents.

It was one of the most widely reported killings in a string of tit-for-tat massacres by pro-government and pro-opposition forces that hardened the conflict's sectarian dynamics. Bayda and the affected neighborhood in Baniyas are predominantly Sunni districts in a coastal region distinguished for its high proportion of Alawites and Christians. Assad is an Alawite, an offshoot of Shiite Islam, and he has crafted the image of his government as a bulwark against Sunni terrorism.

Though the initial protests against him represented a cross-section of Syrian society, the spiraling sectarian violence in 2012 and 2013 fractured the country along religious lines, and now opposition forces are dominated by Sunnis. A similar massacre a year earlier in the town of Houla, near the Lebanese border, also stoked Sunni fears. A U.N. investigation said government forces and pro-Assad militias carried out that attack, which killed 108 people, including 49 children.

Ghouta sarin gas attack

On Aug. 21, 2013, exactly one year and one day after then President Barack Obama issued his "red line" warning against chemical weapons use and transfers, a horrific sarin nerve gas attack killed hundreds of people in the Ghouta suburb of Damascus. Shocking images of residents suffocating in the streets were seen around the world, and one survivor, Kassem Eid, said he saw neighbors dropping dead "like it was judgment day."

In hospitals, medical workers produced videos of victims convulsing and gasping for breath, while others lay motionless, white foam coating their mouths. Doctors lifted patients' eyelids to reveal their pupils shrunken to the size of pinpricks, just like victims of the attack last week in the opposition-held northern Syrian town of Khan Sheikhoun.

A U.N. investigative team determined that sarin gas was used in the Ghouta attack, but its report did not identify a culprit. The U.S. and other nations said Assad's government was responsible. Human Rights Watch said the government was the "likely" culprit and the rockets that carried the gas were likely fired from one or more of a string of military installations that ring the capital.

Napalm-like weapons attacks

Five days after the gas attack on Ghouta, government aircraft bombed a school in the town of Orem al-Kubra, near Aleppo, with a napalm-like weapon, activists reported. Fuel clung to students like jelly, witnesses said, burning skin and flesh. At least 10 people were killed.

Human Rights Watch has documented dozens of attacks where the Syrian government used so-called "incendiary weapons" in the conflict. Their use in civilian areas is against international law.

Schools are also frequent targets of the government's airstrikes.

The siege of east Allepo

After four months of siege and non-stop bombardment, government forces retook the eastern sector of Syria's largest city, Aleppo, last December. By the end of the campaign, every medical facility had been bombed at least once, according to the Syrian American Medical Society.

More than 20,000 civilians and fighters agreed to evacuate from the city to other opposition areas in northern Syria instead of face the government's feared security forces; thousands more crossed first into government parts of the city then continued on to opposition-held Idlib and Aleppo provinces.

A U.N. investigative panel said the evacuation, made under crushing duress, amounted to forced displacement of civilians from their homes, a war crime. Other such actions have dislodged tens of thousands more dissidents to opposition areas of northern Syria, part of a population shift that is changing the demographics of the country.

The U.N. panel also blamed Syrian jets for bombing a humanitarian convoy in the Aleppo countryside during the siege, killing more than a dozen relief workers. It said the attack was a war crime.

Targeting the medical sector

International medical charities say Assad's forces target hospitals, clinics and ambulances in opposition-held areas. Earlier in the conflict, doctors said they were tortured by security forces for helping wounded protesters at anti-government rallies. According to Physicians for Human Rights, government and allied Russian forces have killed 727 medical workers in the course of the conflict.