Mr. Hamdallah continued on to a scheduled appearance in Beit Lahia, at the opening of a long-awaited water-treatment project. “They blew up three cars in my convoy near Beit Hanoun,” he told reporters at the event.
Fatah officials immediately pointed fingers at Hamas. The office of Mahmoud Abbas, the Palestinian Authority’s president and the leader of Fatah, said it “holds Hamas responsible” for the “cowardly attack,” and Hussein al-Sheikh, a member of Fatah’s Central Committee who is the authority’s minister of civil affairs, called Hamas “fully responsible.”
Majid Faraj, the Palestinian Authority’s intelligence chief, who was with Mr. Hamdallah, stopped short of blaming Hamas but noted that the group and its security forces continued to bear “full responsibility for ensuring the safety of the land.”
In a statement, the United Nations special coordinator for the Middle East peace process, Nickolay E. Mladenov, also stressed that Hamas was responsible for enabling the Palestinian government to work “without fear of intimidation, harassment and violence.”
The Hamas spokesman Fawzi Barhoum said, however, that Hamas had no role in the attack. He called the blast an attempt to “tamper with the security of the Gaza Strip” and to “strike any efforts to achieve unity and reconciliation,” and demanded an investigation.
Mr. Barhoum instead sought to blame Israel: He suggested those responsible were “the same hands” who had gunned down Mazen Fakha, a Hamas official responsible for a number of terror attacks, in March 2017, and tried to kill Tawfiq Abu Naim, the head of Hamas’s security forces in Gaza, in October.
Hamas has accused Israel of being behind the attacks on both men, who were freed from Israeli prisons in 2011 in a controversial prisoner swap for the captured Israeli soldier Gilad Shalit.
Mr. Abu Naim, inspecting the scene on Tuesday, similarly said the perpetrators had “executed what the Israeli occupation demands,” but added: “We are sorry for what happened to our brothers in the delegation, including the prime minister.”
Mr. Hamdallah, seemingly undaunted by the attack, said he remained determined to heal the Fatah-Hamas rift in Gaza.
“This will never prevent us from getting rid of the bitter division,” he told reporters. “I say in spite of the explosion today, this won’t stop us carrying on with our mission to achieve unity and end the split.”
Roadside bombs in Gaza are a sensitive subject for the Palestinian Authority and particularly for Mr. Abbas, its president, said Grant Rumley, co-author of a biography of Mr. Abbas, “The Last Palestinian.”
In 2007, several large bombs were planted along the route Mr. Abbas was about to use to attend a meeting with a Hamas leader in Gaza. The bombs were discovered, Mr. Abbas aborted the meeting, and he has not returned to Gaza since, Mr. Rumley said.
The relatively limiteddamage caused by the bomb on Tuesday gave rise to considerable speculation among analysts and officials in Gaza and beyond about who, beside Hamas, might have had reason to set off the device — either as an authentic assassination attempt or, perhaps, to send a message.
In Gaza’s complex political and factional thicket there were no shortage of other potential suspects: Salafi jihadists, who of late have attacked Hamas about as much as they have attacked Israel; allies of Muhammad Dahlan, the exiled Fatah leader who is reviled by Mr. Abbas but widely seen as a potential successor to him; and the Palestinian Authority itself — an embarrassing security lapse could bolster its case that Hamas ought to turn over security control in Gaza to the authority.
Indeed, within hours of the attack and Mr. Hamdallah’s return to the West Bank, Palestinian Authority officials were making precisely that argument in local media coverage.
Later, in Washington, Jason Greenblatt, the president’s Middle East envoy, drew a similar conclusion in opening remarks at the White House meeting: “This attack, once again, demonstrates that Hamas is profoundly unfit to govern Gaza,” Mr. Greenblatt said.
At the blast site in Beit Hanoun, a few hundred yards from the Erez crossing from Israel, windows were shattered in nearby buildings and witnesses reported that a security officer in Mr. Hamdallah’s motorcade had been lightly wounded in the face. Investigators at the scene said the explosive device was planted next to a streetlight, and that a second bomb, powered by 9-volt batteries, was found nearby, less than a foot underground.
Police said that security personnel escorting Mr. Hamdallah had shot at four men on two motorcycles who were seen in the area before the blast, and then arrested them as suspects.
The event Mr. Hamdallah attended on Tuesday was the opening of a long-delayed wastewater treatment plant in Beit Lahia that is intended to serve 400,000 Gaza residents. A temporary arrangement between the Palestinian Authority and Israel is supplying power for the plant, but officials are seeking a dedicated electrical line from Israel as a reliable power source.
Power shortages have routinely caused water treatment to cease, allowing raw sewage to seep into the groundwater and flow into the sea, polluting the local water supply and fouling beaches throughout Gaza and along much of the southern Israeli seashore.