GAZA CITY, Gaza Strip — The eight-month closure of Gaza has created "grim and miserable" conditions that deprive Palestinians of their basic dignity, the U.N.'s humanitarian chief said Friday.

Later Friday, a powerful blast went off in the house of a senior Islamic Jihad activist, killing him, his wife and daughter, and three neighbors, medics and an Islamic Jihad spokesman said. Islamic Jihad said an Israeli airstrike targeted the house, but Israel denied it.

John Holmes, undersecretary-general for humanitarian affairs, visited Gaza during the day and urged that the territory's borders be reopened to relieve the suffering.

Israel and Egypt severely restricted access to Gaza after the Islamic militant group Hamas seized the territory by force in June. Since then, only a few dozen trucks carrying food, medicine and other staples have been permitted into Gaza every day, while most exports are banned.

The closure has driven up poverty and unemployment, and the U.N. says some 80 percent of Gaza's 1.4 million people now get some food aid.

"All this makes for a grim human and humanitarian situation here in Gaza, which means that people are not able to live with the basic dignity to which they are entitled," Holmes told reporters in Gaza.

The extent of suffering in Gaza has been a subject of dispute. Palestinians and human rights groups say hardship is widespread, while Israeli government officials have accused Hamas of trying to manufacture a humanitarian crisis for political gain.

Holmes toured Gaza's largest hospital, speaking with dialysis patients and inspecting the neonatal unit. He also visited an industrial zone that once employed 1,800 Palestinians but has been idled by the border closure.

It was Holmes' first visit to Gaza as humanitarian affairs chief, part of a four-day trip that also includes a a stop in the Israeli town of Sderot, which has been hit hard by rocket fire from Gaza. His four-vehicle convoy, marked by blue U.N. flags, drove through potholed, muddy streets without a Hamas police escort.

The U.N. envoy started the day at Gaza City's Shifa Hospital, where administrators told him they were worried about a possible breakdown of overburdened generators and that they needed spare parts for medical machinery, such as dialysis machines.

In recent weeks, rolling blackouts of several hours a day have been the norm in Gaza, a result of reduced fuel shipments by Israel, which says it is trying to pressure Gaza militants to halt rocket fire into Israel. So far, generators have kept hospitals going during power cuts.

"No freedom, no freedom," Zaher Shabat, the wife of dialysis patient Ahmed Shabat, told Holmes in broken English, after trying to squeeze all her woes into a brief conversation. She told him she has 10 children, and with her husband unemployed, it was tough for him to spend money on trips to the hospital every other day.

"I'll do my best," Holmes told her.

At Gaza's main cargo crossing, closed since June, Holmes was briefed by Wadie al-Masri, general manager of the Karni industrial zone which employed 1,800 before the closure.

Al-Masri said he told Holmes that Israel must significantly increase the number of truckloads allowed into Gaza, from about 50 to at least 200 a day, just to meet basic needs. He said Gaza's private sector has largely collapsed since the closure, and that some leading manufacturers have taken their business abroad.

Holmes called for reopening Gaza, and said he would talk about it with Israeli officials and representatives of the West Bank government of moderate Palestinian President Mahmoud Abbas, Hamas' rival.

"I have been shocked by the grim and miserable things I have seen and heard about during the day," Holmes said.

Israeli government spokesman Mark Regev said an improvement depended on an end to the rocket attacks.

"If terrorists in Gaza were to cease firing rockets into Israel, trying to kill our people, the situation could very quickly return to where it was," Regev said.

In the evening, Islamic Jihad said an Israeli airstrike targeted the house of Ayman Atallah Fayed in the Bureij refugee camp in central Gaza. Fayed is a senior member of the group's military wing and Islamic Jihad said he was among the dead.

The group threatened reprisal attacks against Israel.

But the Israeli military said it had not launched an airstrike on the camp. Witnesses reported seeing fragments of what looked like locally produced rockets at the scene, suggesting the house may have been used to store arms. Hamas police said the cause of the blast was not clear.

Witnesses said the three-story home was flattened by the blast, and six nearby homes were badly damaged. Six people died and at least 40 were wounded, including 12 who were in critical condition.