Aljazeera's correspondent said soldiers on Saturday set up a military checkpoint at the Uthman mosque, dividing the city into two and preventing its residents from moving around.
The exact number of Palestinians detained could not be confirmed due to restrictions on access to the city.
The correspondent said a journalist working for al-Quds newspaper and another with a local television channel were arrested. The Israeli raid was aimed at Palestinian resistance fighters, particularly from the Hamas, he added.
In al-Ain refugee camp, Israeli soldiers fired teargas at residents. No casualties have been reported.
Israeli sources confirmed to Aljazeera that the "military operation" would continue for the next 100 hours.
West Bank curfew
Israeli occupation forces have also imposed a curfew on the city of Tulkaram and set up checkpoints across the West Bank, sealing it off.
Earlier on Saturday, an armed Palestinian reportedly infiltrated a Jewish settlement of Avnei Hafetz in the West Bank, killing a settler and wounding his daughter before soldiers shot him dead, an Israeli army spokesman said.
An unconfirmed number of
Palestinians have been detained
There was no immediate claim of responsibility for the attack.
Palestinians in Jenin city will stage a demonstration on Saturday to commemorate the second anniversary of the Jenin refugee camp massacre, our correspondent reported.
Protesters will head for the camp where unarmed Palestinians were killed during an Israeli invasion in 2002.