A Palestinian protesters burn tyres during clashes with Israeli troops following a protest marking Palestinian "Prisoners' Day", outside Ofer military prison near the West Bank city of Ramallah. Thursday, April 16, 2015 (Photo: AP)

A Palestinian protester throws back a tear gas canister that was fired by Israeli troops during clashes following a protest marking Palestinian "Prisoners' Day", outside Ofer military prison near the West Bank city of Ramallah. Thursday, April 16, 2015 (Photo: AP)

A Palestinian protester returns a gas canister fired by Israeli troops during clashes following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

Protesters wave Palestinian flags during a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

A Palestinian protester returns a gas canister fired by Israeli troops during clashes following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

An Israeli border policeman fires tear gas toward Palestinian protesters during clashes following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

A wounded Palestinian is carried during clashes with Israeli troops following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

A Palestinian protester runs during clashes with Israeli troops following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

A Palestinian protester carries a burning tyre during clashes with Israeli troops following a protest marking Palestinian Prisoners' Day near Israel's Ofer Prison, near the West Bank city of Ramallah April 16, 2015 (Photo: Reuters)

Protesters attend a rally marking Palestinian Prisoners' Day in Gaza City April 16, 2015 (Photo: Reuters)