Arsonists have destroyed a number of shops in the West Bank town of Ramallah during the night.
Ramallah violence follows a Fatah show of strength in Gaza on Sunday
Unconfirmed reports said the shops belonged to supporters of the governing Hamas movement, which is locked in a power struggle with its rival Fatah.
About 30 people have been killed in violence between Palestinian groups in the past month.
Separately, Israeli forces say they detained 21 Palestinians in raids across the West Bank.
Those seized were said to be members of a number of groups, including Fatah, Hamas and Islamic Jihad.
No details were given about why they had been detained. Palestinian reports said several of those held were children.
Also in Ramallah, gunmen opened fire on the car of the former Palestinian finance minister, Salam Fayyad.
Details are unclear, but unconfirmed reports say Mr Fayyad, an independent member of parliament, was not in the car at the time.
In the northern West Bank town of Nablus, deputy mayor Mahdi Hamdali was released, two days after he was kidnapped by unknown gunmen, security sources said.
Correspondents says the kidnapping of such a senior Hamas figure as Mr Hamdali raised fears that the violence could soon spin out of control.