A bomb blast ripped through a bus in Jerusalem on Monday and sparked a fire, wounding at least 21 people, Israeli police said, in an apparent escalation in a wave of violence.
Details were still emerging, but police said a bomb had exploded on one bus in a relatively isolated area of Jerusalem, sparking a fire that spread to another one as well as a car.
Israeli domestic security agency Shin Bet referred to the explosion as a "terror attack".
The bombing was expected to lead to a sharp increase in security ahead of Jewish Passover celebrations beginning Friday night.
If confirmed as a Palestinian bombing, it would both reverse a decline in a wave of violence that erupted in October and mark an escalation, with most of the attacks having been stabbings.
"A professional examination of police sappers has proven that a bomb exploded on the back part of the bus, resulting in the wounding of passengers and the burning of the bus," a police statement.
"In addition, another bus and car were damaged."
An AFP journalist at the scene said one bus was completely burnt out while another was partially burned, with a large contingent of firefighters battling to extinguish the blaze.
Police said 21 people were injured, with medics reporting at least two hurt seriously. Police were investigating whether any of the wounded were behind the bombing.
Authorities initially said most of the wounded were passengers on the second bus, though conflicting information later emerged.
The blast struck in an area of the city without any major buildings or homes and which is not heavily used by pedestrians.
The location was on Moshe Baram Street close to the so-called Green Line dividing mainly Jewish west Jerusalem from predominately Palestinian east Jerusalem.
Jerusalem Mayor Nir Barkat called on residents to be vigilant, "but continue with your plans".
"Here in Jerusalem and in Israel, we go back to normal life as fast as possible," he said.
"It's part of the deep understanding that if it's a terror attack, they want to deter us from our normal life, and what we must do... is go back to normal life as fast as possible."
It was the latest incident in an almost eight-month long surge of Israeli-on-Palestinian deadly repression met with violent responses by Palestinians against settlers and Israeli soldiers.
The recent surge in violence has raised concern of wider escalation, a decade after the last Palestinian uprising subsided.
Since the start of October, Israeli occupation forces have killed at least 201 Palestinians. Meanwhile, almost daily stabbings, shootings and car-ramming attacks by frustrated and unarmed Palestinians have killed 28 Israelis.
The current wave of protests by Palestinians and repression by Israeli occupation forces started in late July when toddler Ali Dawabsha was burned to death and three other Palestinians were severely injured after their house in the occupied West Bank was set on fire by Israeli settlers.
Settlement-building, racial discrimination, confiscation of identity cards, long queues at checkpoints, as well as daily clashes and the desecration of Al-Aqsa mosque, describe Palestinians' daily suffering.
The anger of Palestinian residents of Jerusalem has increased in the last three years after the Israeli authorities allowed increasing numbers of Jewish settlers to storm the Al-Aqsa mosque.
The last bomb targeting a bus in Jerusalem dates back to 2011, when a British tourist was killed.
In Tel Aviv, a bomb exploded on an empty bus in 2013 in what Israeli authorities called a "terrorist" attack.
Suicide bombings were frequent during the second Palestinian intifada between 2000-2005.
Speaking before the bomb was confirmed, police spokesman Micky Rosenfeld said "if it was a terrorist attack, the implications are very great in terms of security on the ground".
The surge in violence has been fuelled by Palestinians' frustration over Israel's 48-year occupation of land they seek for an independent state, and the expansion of settlements in those territories which were captured by Israel in the 1967 Middle East war.
Palestinian leaders say a younger generation sees no hope for the future living under Israeli security restrictions and with a stifled economy. The latest round of US-brokered peace talks collapsed in April 2014.
*The story has been edited by Ahram Online.