Israeli forces faced off with Palestinian stone-throwers in the West Bank during the annual Nakba Day protests over the "catastrophe" that befell the Palestinians in 1948.
At Beitunia checkpoint near Ramallah, youths hurled stones at troops, who fired tear gas, metal pellets and rubber bullets in a bid to break up the demonstration.
Many protesters could be seen with blood on their faces as they waved black flags and roared angry slogans.
Clashes also broke out at Qalandiya checkpoint south of Ramallah, where youths threw stones at Israeli troops, who fired tear gas and rubber bullets to disperse them.
A source at Ramallah's government hospital said that 17 people had been injured by rubber bullets, 15 at Beitunia and another two at Qalandia.
There were also reports of clashes in Hebron and at Rachel's Tomb on the edge of Bethlehem, where the Israeli military said 200 protesters confronted troops.
Demonstrations also took place at the nearby Ofer military prison and Qalandia checkpoint where there were some minor clashes.
Our correspondent Cal Perry in Qalandiya said: "The clashes are very small and very fierce. The Israelis have been firing rubber bullets and tear gas throughout the morning.
"The crowd is expected to grow throughout the day. We are expecting to see things in Jerusalem and Qalandia because it is the crossing between Jerusalem and Ramallah."
A mass rally is scheduled to take place in the Gaza Strip, with smaller protests to be held elsewhere in the West Bank and East Jerusalem.
The Higher Arab Monitoring Committee, which represents Palestinian communities in Israel, has called for a general strike and for Palastinians to visit the sites of former Palestinian villages.
More than 760,000 Palestinians, estimated today to number 4.7 million with their descendants, fled or were driven out of their homes.
About 160,000 Palestinians stayed behind, and now number about 1.3 million, or 20 per cent of the population of "Israel".
Early on Tuesday, an AFP correspondent said clashes broke out between police and demonstrators in the East Jerusalem neighbourhood of Issawiya.
Israel also said a projectile fired from Gaza landed in the country's south, though it was unclear if it was linked to the Nakba commemoration.
"An explosive device fired from the Gaza Strip, a rocket or a mortar shell, landed early this morning in southern Israel, causing no injuries or damage," Micky Rosenfeld , Israeli police spokesman, told AFP.
Israeli security forces are on alert and Nakba Day commemorations in the past have often resulted in clashes with troops and police.
"We are co-ordinating with the military and border police, we hope things will be quiet," Rosenfeld said on Monday. "We have mobilised a number of units in various areas," he said, without elaborating.
Last year, Israeli troops opened fire on demonstrators from Lebanon and Syria as they tried to breach a security fence and enter Israel.
Four protesters from Syria were killed along with another 10 from Lebanon.
A senior military official in Israel's northern command said troops had trained to handle all situations, although they were not aware of plans for any big demonstrations along the borders.
"We are getting ready for all kinds of provocations," he told AFP on condition of anonymity.
This year's Nakba events come with protesters hailing a mass hunger strike by Palestinian prisoners in Israeli jails.
The strike appeared to have come to an end on Monday night after an Egyptian-mediated deal under which Israel offered a number of measures easing prison conditions in exchange for an end to the hunger strike.