JERUSALEM  The killing of four Israeli settlers, including a pregnant woman, in the West Bank on Tuesday evening rattled Israeli and Palestinian leaders on the eve of peace talks in Washington and underscored the disruptive role that the issue of Jewish settlements could play in the already fragile negotiations.

The military wing of Hamas, the Islamic group, claimed responsibility for the attack  in which gunmen fired on a vehicle carrying two men and two women at a junction near the city of Hebron  and described it on its Arabic Web site as a “heroic operation.”

Prime Minister Benjamin Netanyahu condemned the “atrocious murder,” which Israeli officials said seemed calculated by Hamas to upset the negotiations, which it virulently opposes. Mr. Netanyahu, en route to Washington at the time, said, “Terror will not determine the borders of Israel or the future of settlements.” He ordered Israel’s security forces “to pursue the attackers without any diplomatic restraint,” his office said.

The Palestinian Authority also condemned the attacks, which occurred just before its president, Mahmoud Abbas, met with Secretary of State Hillary Rodham Clinton. A Palestinian spokesman, Nabil Abu Rudeineh, said the attack by Hamas, the authority’s rival, underlined “the need to proceed quickly toward a just and lasting peace agreement,” which he said would “put an end to these acts.”