The United States strongly condemned the attack Tuesday in which four Israelis were shot dead near the Kiryat Arba settlement in the West Bank, dpa reported.
The attack came just ahead of Thursday's resumption of Israeli- Palestinian direct peace negotiations in Washington.
"The United States condemns in the strongest possible terms the terrorist attack today perpetrated by Hamas," the White House said in a statement, calling for the "terrorists behind this horrific act to be brought to justice."
The attack was also condemned by the Palestinian Authority and the United Nations.
On the eve of the first face-to-face talks between Israel and the Palestinians in nearly two years, "this brutal attack underscores how far the enemies of peace will go to try to block progress," the White House said.
"It is crucial that the parties persevere, keep moving forward even through difficult times, and continue working to achieve a just and lasting peace in the region that provides security for all peoples."
Israeli security forces will "exact a price from the murderers," Israeli Defence Minister Ehud Barak was quoted as saying by The Jerusalem Post.
Barak, who spoke with Israeli Prime Minister Benjamin Netanyahu who was en route to Washington, described the attack as "likely an attempt by the low-life terrorists to prevent the diplomatic process and to hurt the chances of the talks opening in Washington."
An unidentified member of Netanyahu's staff was cited by the Ynet Israeli news site as saying the talks would go ahead as planned.
Palestinian Prime Minister Salam Fayyad said: "We condemn this operation, which contradicts with Palestinian interests and efforts by the Palestinian leaders to gain international support for the rights of our people."
An Israeli military spokeswoman said two women and two men were killed while riding in a car at the Bani Naim intersection near Kiryat Arba, an Israeli settlement located just outside the city of Hebron. She said that the attacker or attackers opened fire from a hiding spot.
According to Israeli media, one of the dead was a pregnant woman. All four victims were believed to be from the same family.
The military wing of the Islamist Hamas movement, Izeldein al- Qassam Brigades, claimed responsibility for what it called a "heroic attack."
The group said earlier that the attack was "a natural response to the crimes of the Israeli occupation and its settlers. ... It is a reiteration that the armed Palestinian resistance is present despite the war to uproot it."
The attack recalled the kind of violence of the Palestinian Intifada, or uprising, a decade ago in the West Bank. In recent years, however, the region had become relatively more peaceful.
It came on the day that US Secretary of State Hillary Rodham Clinton started a series of meetings with Middle East leaders in Washington ahead of direct talks.
US President Barack Obama will on Wednesday host a dinner at the White House to be attended by Abbas, Netanyahu, Egyptian President Hosny Mubarak and Jordan's King Abdullah II.
Clinton will open the direct peace talks on Thursday.