Three Israelis have been killed and four wounded near a settlement in the West Bank, Israeli sources say.
The shootings broke a period of relative calm
The gunmen shot from a passing vehicle at a bus stop outside Gush Etzion, a major settlement bloc. Another Israeli was wounded in a separate shooting.
Israel Radio said militants of the al-Aqsa Martyrs' Brigades had admitted carrying out the Gush Etzion attack.
Israeli troops later killed a leader of Islamic Jihad near the northern West Bank town of Jenin during a shootout.
The shootings have broken a period of relative calm in the region since Israeli troops completed their withdrawal from the Gaza Strip on 12 September, says the BBC's Ian Pannel in Jerusalem.
The Israeli authorities say the attacks highlight the dangers of easing restrictions in the area and have told the Palestinian Authority to do more to control the militants.
Certainly the incident comes at a sensitive time, with Palestinian leader Mahmoud Abbas heading to Washington later this week for a meeting with President George W Bush to discuss the issue of peace in the region, our correspondent says.
"A Palestinian passed by in a car, let off a burst of fire, and struck down people standing at the hitchhiking post," Shaul Goldstein, a settler leader in Gush Etzion, told Israel Radio.
A large number of Israeli troops have been sent to the area near Bethlehem to look for the attackers.
The second attack took place near the settlement of Eli in the northern West Bank. Israeli rescue services said one Israeli was seriously wounded.
Al-Aqsa militants in Jenin have announced an end to their truce
The Islamic Jihad militant was killed during a clash near Jenin.
Palestinian hospital officials said Nihad Abu Ghanim, 27, died after being shot in the head, abdomen and chest.
He was the top Islamic Jihad militant in the northern West Bank town of Burkin.
Israeli military officials said that Abu Ghanim was killed when Israeli troops spotted an armed Palestinian during a routine patrol.
Palestinian militant factions began a ceasefire early this year, but low-level violence has continued.
After an Israeli raid which killed three militants early this month, al-Aqsa militants in Jenin said they were ending their truce.