More than 20 people died on Thursday as Syrian government planes continued to attack eastern Ghouta, a rebel-held suburb of Damascus, with a barrage of airstrikes.
The airstrikes are part of an onslaught that has stretched on since Monday, NPR's Ruth Sherlock reports from Beirut.
"Local monitoring groups are reporting that just today, 21 people were killed and 125 others injured, including women and children," Ruth says. "That brings the total number of deaths to at least 167 people in last four days.
"The U.N. appealed on Tuesday for an immediate halt to the bombardment. But so far, the calls have not been heard."
Ruth says that eyewitness video shows a familiar pattern: A bomb dropped, first responders rushing to extract survivors from rubble. "White dust and screams are everywhere," she says. "And repeat."
As Ruth reported on Wednesday, intensifying government attacks on civilians — including the bombings in eastern Ghouta, multiple attacks in Idlib and reported chlorine gas attacks — "have been interpreted partly as a response to the rebel downing of a Russian Su-25 plane Saturday near Saraqeb." She continues:
"The Russian pilot ejected from the plane and was shot dead by militants, according to Russia's Defense Ministry.
"Kremlin spokesman Dmitry Peskov called the attacks 'precision strikes,' according to Russia's TASS news agency, and said they were "provoked by the tragic event when terrorists shot down our plane."
"But analysts also see these attacks as an attempt to punish opponents of Syrian President Bashar Assad by targeting towns and villages in Syria that are sympathetic to the opposition.
Meanwhile, in eastern Syria, the regime is accusing the U.S. of "aggression" after the Syrian government and the U.S.-led coalition exchanged direct attacks in Deir el-Zour province.
The conflict in Syria is many-sided, with complex battle lines between multiple rebel factions, Islamist groups, government-backed troops and U.S. and Russian forces.
It has been rare for regime and U.S. forces to directly target each other, as NPR's Tom Bowman reported Wednesday.
But on Wednesday, as we reported, regime-backed forces attacked Syrian opposition troops, accompanied by U.S. advisers. One rebel was wounded, but there were no American casualties, Tom reported.
The Pentagon called it an "unprovoked attack" and responded with airstrikes against the regime-backed troops.
Those attacks killed about 100 Syrian soldiers, the U.S. military said.
In response, Syrian state media called the U.S. attack an "aggression" and a "new massacre," the AP writes.
The attack "adds another layer to a conflict in Syria that is once again plunging into a new unpredictable spiral of violence," as the AP puts it.
And in northern Syria, the battlefield is growing increasingly complex. As the U.S. tries to keep the focus on the fight against ISIS — which has been routed out of its former Syrian strongholds — tensions are growing between Kurdish and Turkish forces, both of which are allied with the Americans.
You can hear more about the situation in northern Syria in the latest dispatch from Tom Bowman, who is on the ground with American forces.