The BBC reports that the Abu Ali Mustafa Brigades, the military wing of the Popular Front for the Liberation of Palestine, says it carried out the brutal attack at a Jerusalem synagogue this morning that killed four Israelis and wounded eight others.
The PFLP is a Marxist-Leninist organization that some on the anti-Zionist Western Left, who consider Fatah a sellout and who are uncomfortable with the theocratic nature of Hamas, support enthusiastically.
See, for example, here, here, here and here.
Update: The Washington Post reports:
[T]he Popular Front for the Liberation of Palestine claimed responsibility, but that assertion soon came under suspicion as relatives of the Palestinian assailants said the men worked alone.
However the PFLP did call the synagogue attack a “heroic operation.”
Also, Shin Bet head Yoram Cohen contradicted claims by Prime Minister Benjamin Netanyahu and Defense Minister Moshe Ya’alon that Palestinian Authority President Mahmoud Abbas was deliberately inciting violence.
Further update: Secretary of State John Kerry takes a lot of flack for his criticisms of the Netanyahu government. Here he calls out the Palestinian leadership.