Al Aqsa Martyrs Brigade, a militant group in Palestinian President Mahmoud Abbas's West Bank-based Fatah movement, claimed responsibility for the rocket strike, the Palestinian Ma'an news agency said. No casualties were reported.
Hamas, the Islamist group that controls the Gaza Strip, said it was investigating. There was no military response from Israel after the rocket slammed into a road near its southern city of Ashkelon.
The rocket was the first to hit Israel since a November 21 truce brokered by Egypt ended eight days of air strikes and missile attacks in which 175 Palestinians and six Israelis were killed.
Yesterday's strike came after a surge of unrest in the occupied West Bank raised fears in Israel of a new Palestinian intifada, or uprising.
On Monday, thousands of Palestinians in the West Bank turned out for the funeral of Arafat Jaradat, 30, who died in disputed circumstances in an Israeli prison on Saturday.
Israeli police shot and wounded five Palestinian youths during confrontations in Bethlehem and outside a West Bank prison later the same day, leaving a 15-year-old boy in a critical condition.