Palestinian Prime Minister Rami Hamdallah, center left, is surrounded by body guards as he arrives for the opening ceremony of a long-awaited sewage plant project, east of Jebaliya, in the northern Gaza strip, Tuesday, March 13, 2018. An explosion occurred as the convoy of the prime minister entered Gaza through the Erez crossing with Israel. The Fatah party of the prime minister called the explosion an assassination attempt and blamed Gaza militants. (AP Photo/Adel Hana)

Palestinian Prime Minister Rami Hamdallah, center left, is surrounded by body guards as he arrives for the opening ceremony of a long-awaited sewage plant project, east of Jebaliya, in the northern Gaza strip, Tuesday, March 13, 2018. An explosion occurred as the convoy of the prime minister entered Gaza through the Erez crossing with Israel. The Fatah party of the prime minister called the explosion an assassination attempt and blamed Gaza militants. (AP Photo/Adel Hana)

JABALIYA, Gaza Strip (AP) — A roadside bomb on Tuesday struck the convoy of the Palestinian prime minister during a rare visit to the Gaza Strip, causing no serious injuries but throwing an already troubled reconciliation process between rival factions into deeper turmoil.

Prime Minister Rami Hamdallah had just arrived from his West Bank headquarters to attend a ribbon-cutting ceremony for a new water-treatment plant when the bomb went off. Although there was no claim of responsibility, Palestinian officials accused Gaza militants of trying to assassinate Hamdallah. Gaza’s ruling Hamas group denied involvement.

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The blast took place at a time of deadlock in reconciliation efforts between Hamdallah’s Fatah party and Hamas, which has controlled Gaza since ousting Fatah forces in 2007. It also cast a shadow over a special White House meeting where international donor nations were set to discuss the dire humanitarian situation in Gaza.

Hamdallah, a soft-spoken former university dean appointed by President Mahmoud Abbas five years ago, went on to inaugurate the long-awaited sewage plant project. But he quickly returned to the West Bank, where he vowed to press ahead with reconciliation efforts.

“This will not deter from seeking to end the bitter split. We will still come to Gaza,” he said.

He said the attack underscored the need for the Palestinians to unify under a single authority. Hamas has ceded some government functions and control of Gaza’s borders, but it has refused calls to disarm and let Palestinian Authority security forces take over.

“How can a government overtake Gaza without maintaining security? We ask Hamas one more time to empower the government,” he said. “Without security, there won’t be a government or an authority.”

Hamas condemned the attack, calling it a crime and an attempt to “hurt efforts to achieve unity and reconciliation.” It promised an “urgent” investigation.

Witnesses said the bomb was planted under an electric pole on Gaza’s main north-south road and went off shortly after Hamdallah’s 20-vehicle convoy had entered through the Israeli-controlled crossing.

“I could not see anything because smoke and dust filled the air. When the smoke cleared, the explosion was followed by heavy gunfire, apparently from police securing the convoy,” said a witness, who declined to be identified because of security concerns. “When the dust cleared, I saw people running everywhere, and police were running around.”

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Two vehicles were disabled by the blast, while at least four others were damaged, with windows or sunroofs blown out. One had streaks of blood on the door. Hamdallah said six bodyguards required medical attention.

In the West Bank, Abbas blamed Hamas for the blast. But his security chief, Majed Farraj, who was in the convoy and was another potential target of the blast, said it was “too early” to say who was responsible.

There is a long list of potential attackers. While Hamas officials strenuously denied involvement, there are elements within the group that do not want to cede power and oppose the reconciliation process. More radical militants, inspired by the Islamic State group, also operate in Gaza. Some even suggested that the Palestinian Authority had staged the incident to shore up Hamdallah’s calls for Hamas to disarm.

The 2007 Hamas takeover left the Palestinians with two rival governments, Hamas in Gaza and the Western-backed Palestinian Authority governing autonomous enclaves in the Israeli-occupied West Bank. Repeated attempts at reconciliation have failed or stalled.

In November, Hamas handed over control of Gaza’s border crossings to the Palestinian Authority. It was the first tangible concession in years of Egyptian-brokered reconciliation talks. But negotiations have bogged down since then.

Hamdallah’s visit came at a time of crisis in Gaza. The economy has been devastated by three wars between Hamas and Israel and a decade-long blockade by Israel and Egypt meant to weaken the militant group.

Amid warnings of a looming humanitarian catastrophe, the White House was hosting a gathering of international representatives Tuesday to discuss economic development projects and the dire situation. The Palestinian Authority, still angry over the U.S. decision to recognize Jerusalem as Israel’s capital, did not attend.

The U.S., Israel and other Western allies consider Hamas a terrorist group and want assurances that any development aid does not bolster Hamas or get diverted for military purposes.

In Washington, White House envoy Jason Greenblatt criticized Hamas for wreaking devastation on the territory through its rule and expressed regret that the Palestinian Authority was not attending.

“This attack, once again, demonstrates that Hamas is profoundly unfit to govern Gaza,” he said in Washington. “But we cannot be deterred, and the Palestinian Authority should not be deterred.”

The European Union’s foreign policy chief, Federica Mogherini, called the attack a “deliberate attempt” to undermine reconciliation.

“For the European Union it is clear: those who work to exacerbate divisions through violence are working against the interest of the people of Gaza and of all Palestinians,” she said.

The United Nations Mideast envoy also condemned the attack. Nickolay Mladenov said until the “legitimate” Palestinian Authority takes power in Gaza, Hamas is responsible for enabling the internationally backed government to work without fear of intimidation, harassment and violence.

The sewage plant was envisioned in 2007 after overburdened sewage reservoirs collapsed, causing a flood that drowned five villagers.

The World Bank, European Union and other European governments have provided nearly $75 million in funding for the project. The Hamas takeover, the ensuing Israeli-Egyptian blockade, power shortages and conflicts delayed the opening for four years.

Besides the old reservoirs, the plant will receive wastewater from four towns and villages. After treatment, the water will be transferred for irrigation and the remainder will be safely dumped into the sea.