Deadly drive-by shootings by Hamas gunmen this week proved that the Palestinian militant group can still operate in the West Bank when its leadership demands, despite a sustained crackdown by Israel and the Palestinian Authority.

Hamas has pledged to follow up on the attacks, which appeared timed to the re-launch in Washington of direct peace negotiations between Israel and the Palestinian Authority.

For more than two years, Israelis and Palestinians have celebrated the relative quiet that has prevailed in the West Bank and applauded the U.S.-trained Palestinian security services, which have fought, arrested and disarmed Hamas and other militants in coordination with Israel.

Palestinian officials have described the establishment of a credible security service and rule of law as an important precursor to statehood and have voiced pride in their successes.

The three attacks Tuesday, Wednesday and Thursday, which left four Israelis dead and two wounded, seemed like an anomaly amid the recent calm.

They were, however, reminiscent of routine attempts in the 1990s by Hamas's military wing, the Izzedine al-Qassam Brigades, to disrupt peace efforts and raised new questions about the group's strength in territory the Palestinians want for their future state.

"There is no doubt that [the Brigades] are being chased by the Authority and the occupation, and our circumstances are hard," Abu Ubaidah, a spokesman for the Brigades, said in an interview Thursday in Gaza. But this week's attacks show there is a "possibility" and a "will to carry out operations," he added.

Hamas remains "a substantial power" in the West Bank and "should not be underestimated" there, Ghassan Khatib, a spokesman for the government of Palestinian leader Mahmoud Abbas, acknowledged in an interview Thursday.

"However, I think the public is not in the mood to support resuming violent attacks against Israelis," Khatib said. "The general opinion is the intifada was not compatible with the interests of the Palestinian people."

Considered a terrorist group by the United States, Israel and others, Hamas is thought to get much of its funding from Iran.

The Islamist group, which opposes peace negotiations with Israel, has controlled the Gaza Strip since 2007, when it defeated Abbas's Fatah forces in a bloody power dispute.

Since then, the two main Palestinian factions have failed to reconcile, and Hamas has become as much an enemy of Abbas as it has of Israel.

Hamas's military wing takes its guidance from the organization's political leaders, who live in Gaza and Syria. Abu Ubaidah said the military wing's operations have to be "in harmony with the attitude of the political wing."

To protect themselves from Israeli retaliation, Hamas's political leaders have long sought to keep vague how much direction they give militants. The military wing's own leader, Mohammed Deif, is so fearful of assassination that he is never seen in public.

As it has grown as a political entity, Hamas has shifted its tactics against Israel.

Mass-casualty suicide bombings targeting Israeli civilians from the 1990s through 2007 gave way to rocket attacks from Gaza after Israel and the Palestinian Authority cracked down on Hamas's infrastructure in the West Bank and drove many of its operatives underground.

By early 2009, as Israel waged a punishing military campaign in Gaza after a long period of rocket fire, Hamas operatives in the West Bank were unable to retaliate.

Hamas subsequently worked to redevelop its capabilities in the West Bank, a senior Israeli military officer said. "The results are what we've seen in the past few days," he said.

Since Tuesday's attack, Palestinian security services have detained about 300 Hamas members in the West Bank.

Palestinian officials said they should not be blamed for the attacks, since the shootings took place in areas where Israel still has exclusive control of security. Israeli officials claimed the shooters came from Palestinian-controlled areas and fled back there.

Hamas has the capacity to carry out more attacks in the West Bank, especially drive-by shootings that require little manpower or planning, Israeli and Palestinian security officials acknowledged this week.

But the group's ability to reach inside Israel proper may be curtailed, they said, because of Israeli and Palestinian counterterrorism measures, including the barrier Israel has built between Israel and the West Bank.