The spokesman said an attack on the consensus government is an attack on the unity of the Palestinian people.
The blast occurred shortly after the convoy entered Gaza, but no injuries were reported, said the sources. Hamas' takeover of Gaza from the Palestinian Authority in 2007 and the ensuing Israeli-Egyptian blockade, power shortages and conflicts delayed the opening of the project for four years.
Hamdallah appeared on television shortly after the explosion as he opened a plant in the territory.
He had been expected to hold a number of other engagements before leaving.
Hamas criticised Abbas's accusation, saying it "achieved the goals of the criminals".
Hamdallah was visiting Gaza in order to attend the inauguration of a wastewater treatment plant and meet officials, reports Efe news agency.
It is Hamdallah's second visit to the Gaza Strip since the signing of an Egyptian-brokered "reconciliation" agreement between the West Bank's governing Fatah faction and Gaza's Hamas rulers late past year.
The incident took place amid heightened tensions between the main Palestinian factions over the implementation of a reconciliation deal signed past year.
In November, Hamas handed over control of Gaza's border crossings to the Palestinian Authority.
Hamas seized Gaza from the PA in a near civil war in 2007 and multiple attempts at reconciliation have since failed. "We will still come to Gaza".
Hamdallah's government is recognised by the global community, while Hamas is blacklisted as a terrorist organisation by the European Union and the United States.
The ties between Palestine and the United States have been witnessing rising tensions since last October, and peaked when U.S. President Donald Trump recognized on December 6, 2017 Jerusalem as a capital of Israel and ordered the moving of the U.S. embassy to the city.