The Hamas Islamic militant movement that controls the Gaza Strip announced Saturday it had chosen its former Gaza prime minister Ismail Haniyeh as the group’s new political chief.

Israel, along with Egypt, has been enforcing a crippling border blockade against them since then. Though it has softened some of its rhetoric, Hamas’ new platform clung to the hard-line positions that led to its isolation. The group reaffirmed it will not recognize Israel, renounce violence or recognize previous interim Israeli-Palestinian peace deals the West’s long-standing conditions for dealing with Hamas.

In its founding charter, Hamas called for setting up an Islamic state in historic Palestine, or the territory between the Mediterranean and the Jordan River, which also includes Israel.

Over the years, Hamas has carried out shootings, suicide bombings and rocket attacks against Israel. Since 2008, Israel and Hamas militants in Gaza have fought three cross-border wars. Mr. Abbas has been an outspoken opponent of violence, saying it undercuts Palestinian interests. Repeated reconciliation efforts between the Palestinian factions have failed.

In February, the group chose militant commander Yehiya Sinwar, one of its most hard-line figures, as its new Gaza chief in charge of the group’s core power base.

In 2006, after Hamas won the legislative elections, Mr. Haniyeh was chosen by the movement to form its first government. He resigned as prime minister after Hamas and Fatah agreed to form a unity government in 2014 a government has never took hold.

For the past four years he has served as Mr. Mashaal’s deputy.

In the past, Hamas has sharply criticized Mr. Abbas’ political program, which rests on setting up a Palestinian state in the West Bank, Gaza Strip and east Jerusalem, lands Israel captured in the 1967 Mideast War.