An injured woman reacts at a site hit by airstrikes in the rebel-held area of Old Aleppo, April 28, 2016.

Fighting raged, with the government claiming rebel shells had killed at least 30 people as they left a mosque, and rebels reporting new government airstrikes.

Syrians help a wounded youth following an air strike on the Fardous rebel held neighborhood of the northern Syrian city of Aleppo on April 26, 2016.

The strikes on the hospital, specializing in pediatric care, hit shortly before midnight April 27, according to opposition activists and rescue workers. They struck a well-known field hospital in the rebel-held district of al-Sukkari in Aleppo. The dead included the last pediatrician remaining in the city’s opposition-held areas and a dentist, activists and a British surgeon who knows the hospital told CBS News.

A boy injured in a strike that destroyed the al-Quds hospital in southern Aleppo, Syria, receives treatment at another facility in the front-line city, in a screen grab from video posted online by Syrian opposition activist group Buraq Media Foundation, April 28, 2016.

The French news agency AFP reported, citing an anonymous Syrian official, the army was preparing to launch a massive offensive to retake the entire city of Aleppo in the coming days.

An explosion rocks the Syrian city of Kobane during a reported suicide car bomb attack by the militants of Islamic State (ISIS) group on a People's Protection Unit (YPG) position in the city center, as seen from the outskirts of Suruc, on the Turkey-Syria border, October 20, 2014 in Sanliurfa province, Turkey.

Kurdish forces recaptured the town on the Turkish frontier on January 26, 2015, with the help of American airstrikes. It was a symbolic blow to the jihadists who have seized large swathes of territory in their onslaught across Syria and Iraq.

Syrian rescue workers and citizens evacuate people from a building following a reported barrel bomb attack by Syrian government forces on the central al-Fardous rebel held neighborhood of the northern Syrian city of Aleppo on June 9, 2015.

Musa, a 25-year-old Kurdish marksman, stands atop a building as he looks at the destroyed Syrian town of Kobane, also known as Ain al-Arab, on January 30, 2015.

Eighty percent of the buildings and infrastructure has been destroyed.

Residents wait in line to receive food aid distributed in the Yarmouk refugee camp on January 31, 2014 in Damascus, Syria.

An estimated 18,000 people were besieged inside the camp in desperate conditions in 2014. The UN called for the Syria regime and rebels to allow food and medical aid into the Palestinian camp of Yarmouk. ISIS recaptured 90 percent of the camp in 2015 leading to worsening conditions for those still trapped there.

A Syrian man reacts while standing on the rubble of his house while others look for survivors and bodies in the Tariq al-Bab district of the northern city of Aleppo on February 23, 2013.

The siege of Aleppo caused a humanitarian catastrophe. The Syrian government escalated the situation in 2012 with the use of barrel bombs, frequently hitting civilian targets. Russian airstrikes beginning in late 2015 intensified an already horrific situation. The vast majority of victims have been civilians. According to the UN some 300,000 people still live in the once thriving city.

An image posted online by the ISIS branch in the Syrian province of Homs appears to show the destruction by explosives of the ancient Baalshamin Temple, in the ruins at Palmyra, 215 kilometers (134 miles) northeast of Damascus.

Syria's fabled desert oasis of Palmyra, a World Heritage site, saw its last tourist in September 2011, six months after the uprising began. Its most recent visitors are violence and looting. ISIS militants destroyed the Baalshamin Temple, Temple of Bel and beheaded a local antiquities scholar. The group also destroyed the 1,800 year-old Arch of Triumph.

UNESCO said ISIS was engaged in the "most brutal, systemic" destruction of ancient sites since World War II.

A Kurdish refugee mother and son from the Syrian town of Kobani walk beside their tent in a camp in the southeastern town of Suruc on the Turkish-Syrian border on October 19, 2014 in Sanliurfa, Turkey. In four weeks more than 200,000 people from Kobani fled into Turkey.

Turkey has given shelter to the largest number of Syrian refugees in the world, an estimated 1.7 million as of mid-March according to the UN.

A rebel fighter holds a position in al-Mayasat, a rebel-controlled area near the industrial zone of the northern Syrian city of Aleppo on February 4, 2015.

Nearly four million people have been forced by war to flee Syria altogether, and millions more are living in misery in areas that have fallen out of government control.

A wounded Syrian girl looks on at a make-shift hospital in the rebel-held area of Douma, east of the capital Damascus, following shelling and air raids by Syrian government forces on August 22, 2015.

According to Unicef, an estimated 3.7 million children, one-third of all Syrian children, were born during the five years of conflict, with more than 300,000 of that number born as refugees, knowing little more than death, destruction and deprivation.

Civil defense members and civilians search for survivors under the rubble of a site hit by what activists said were internationally banned cluster bombs dropped by Russian air force in Maasran town, south of Idlib, Syria on October 7, 2015.

According to a Human Rights Watch report, at least 14 barrel bomb attacks since January 26, 2016 alone.

Russian President Vladimir Putin ordered the country's military to begin pulling out of Syria starting March 14, 2016, stating Russia had accomplished its goals.

A refugee from Syria prays after arriving on the shores of the Greek island of Lesbos aboard an inflatable dinghy across the Aegean Sea from from Turkey on September 7, 2015.

More than 230,000 people landed on Greek shores in 2015, many fleeing war in Syria. Europe now faces the largest migration crisis on the continent since World War II.

People demonstrate against Syria's President Bashar al-Assad on March 15, 2014 in Rome, during a protest to mark the third anniversary of the start of the conflict.

A Syrian woman comforts her children after their house in the Sahour nieghbourhood of the northern Syrian city of Aleppo was bombed on May 14, 2014.

Once home to some 2.5 million residents and considered Syria's economic powerhouse, Aleppo has been divided between government and opposition control since shortly after fighting there began in mid-2012.

French soldiers prepare a Rafale fighter jet at a military base at an undisclosed location in the Gulf on November 17, 2015, as the French army conducts operations against ISIS in Syria and Iraq.

French warplanes destroyed a command center and training center in the Syrian city of Raqa, the stronghold of IS, in its second series of airstrikes in 24 hours, the French defense ministry said.

In the wake of the Paris terror attacks of November 2015, France, Germany and the U.S. among others stepped up the fight against ISIS in Syria.

A man carries a young girl who was injured in a reported barrel-bomb attack by government forces on June 3, 2014 in Kallaseh district in the northern city of Aleppo.

Some 2,000 civilians, including more than 500 children, have been killed in regime air strikes on rebel-held areas of Aleppo since January 2014, many of them in barrel bomb attacks.

Activists carry a Free Syrian Army flag during a protest against forces loyal to Syria's president Bashar al-Assad in the rebel-controlled area of Jobar, a suburb of Damascus, Syria on March 3, 2016.