Israeli security forces confronted Palestinian demonstrators marking "Nakba Day" on Sunday at one of the West Bank's most infamous checkpoints.
The Qalandia checkpoint and crossing is a massive security terminal built into Israel's concrete separation wall dividing Ramallah from Jerusalem and the southern West Bank, and is a frequent flashpoint for protests.
On Sunday, as simultaneous demonstrations throughout the region commemorated the 1948 displacement of 700,000 Palestinians during the creation of Israel, Israeli forces crossed the barrier into the Palestinian refugee camp of Qalandia and fired tear gas and rubber-coated steel bullets at hundreds of demonstrators who responded with stones in a day-long battle.
Palestinian medics evacuated dozens of people who succumbed to the heavy use of tear gas, including many in the nearby refugee camp not involved in the demonstrations.
"I have not seen this many casualties in one day since the Second Intifada," said Dr Sami Dar Nakhla, director of the field hospital. In total, more than eighty protesters received treatment, of which twenty were hospitalised - including three paramedics.
Dr Dar Nakhla said he found evidence of the army using new and brutal forms of crowd control.
"This teargas is toxic, it is the first time I have seen it. It is causing fits, seizures and unconsciousness," he declared.
As many as 40 people were injured by rubber-coated steel bullets, according to reports, and there were numerous violent arrests.
In the late afternoon, undercover Israeli units dressed as Palestinian demonstrators - and at least one dressed as an elderly woman - turned on the crowd and made a series of dramatic arrests at gunpoint as Israeli troops advanced in an unsuccessful bid to end the protest.
Sunday's Nakba Day commemoration included protests elsewhere in the West Bank and Gaza, as well as in Palestinian refugee communities in neighbouring Syria, Lebanon, Jordan, and Egypt.