(Adds more arrests of rocket squad members, paragraphs 1, 3)

GAZA, July 10 (Reuters) - Hamas arrested seven Palestinians who fired rockets into Israel from the Gaza Strip on Thursday, a militant faction said, in the first such detentions since the Islamist group and Israel agreed a truce last month.

Al-Aqsa Martyrs Brigades, a group linked to President Mahmoud Abbas's Fatah group, said Hamas men pursued three of its its members after the attack and "abducted them" in Jabalya refugee camp.

No one was hurt in the strike with two rockets on southern Israel.

Four more men were arrested as they tried to fire rockets at Israel after darkness fell, an al-Aqsa official said.

"We demand their immediate release," said Abu Qusai, a brigades spokesman.

Hamas official Sami Abu Zuhri said: "We stress that all parties should maintain the national agreement that was reached with a consensus."

Hamas, which seized control of the Gaza Strip a year ago after routing forces loyal to the secular Fatah group, had previously said it would not use force against other militants who violate the truce.

Al-Aqsa said it launched the rockets in retaliation for the Israeli army's killing of an unarmed member of the group as he tried to cross a border fence into Israel earlier in the day. His death marked the first fatality along the Israel-Gaza border since the June 19 Egyptian-brokered ceasefire.

An Israeli army spokesman said soldiers shot the man after he ignored their calls to stop and only saw later that he had been unarmed.

NABLUS VISIT

The ceasefire deal calls on Hamas to prevent cross-border rocket fire and attacks from the Gaza Strip, and for Israel to halt its raids and ease an economic blockade.

"If a total cessation of fire from Gaza, as committed in the calm, is not implemented, the calm has no possibility to succeed," Israeli Prime Minister Ehud Olmert's spokesman, Mark Regev, said.

Israel tightened restrictions on the passage of people and goods to and from the impoverished territory after Hamas's takeover. U.N. officials said Gaza's goods crossings were still shut often despite the truce.

"There is not enough fuel, not enough food, there is not enough of anything," John Ging, an official with the U.N. Relief and Works Agency (UNRWA) that aids refugees, said in Gaza.

Although Israel has responded to cross-border rocket fire by frequently shutting Gaza's crossings, records compiled by Western officials show up to a 44 percent increase in goods imports in recent weeks, including a 30 percent rise in fuel.

In the occupied West Bank, Palestinian Prime Minister Salam Fayyad visited Nablus, where Israeli troops had raided several charity groups and a medical clinic and closed down a television station. Israel has raided 15 Nablus charities suspected of being linked to Hamas.

Speaking to shop owners inside a mall Israel ordered closed, Fayyad said: "It should be known clearly that the Israeli army orders and decisions are not valid and don't have any basis. We will deal with them as if they don't exist."

"Shopkeepers are invited to open their stores and ignore the Israeli decision," he added.

Senior Hamas leader Ismail Haniyeh accused Palestinian Authority officials of backing the Israeli operations. (Additional reporting by Atef Sa'ad in Nablus and Mohammed Assadi in Ramallah; Writing by Jeffrey Heller in Jerusalem)