Israel’s accusations against 12 employees of the U.N. aid agency for Palestinians, the main aid operation in Gaza, are the latest episode of a decades-long friction between Israel and the group.

The United Nations Relief and Works Agency, known as UNRWA, is one of the oldest U.N. agencies, founded in 1949 to care for Palestinian Arabs who had fled or been forced from their homes during the wars surrounding the creation of the state of Israel in the late 1940s. When a separate U.N. agency was later founded for refugees of other conflicts, UNRWA remained independent.

To Palestinians and their supporters, the group remains an essential lifeline for millions of descendants of those refugees, whose status and future has never been resolved in negotiations between Israeli and Palestinian leaders. It is one of the largest employers in Gaza, with 13,000 people, mostly Palestinians, on staff.

Many of them live in underdeveloped urban neighborhoods — still known as refugee camps — in cities across the Middle East. In Gaza, they form the majority of the population, and UNRWA plays a pivotal role in providing them with education, social services and — during the current war — aid and shelter.

“Because their plight as refugees has never been resolved, they continue to be refugees,” said Chris Gunness, a former spokesman for UNRWA.

“These are some of the most vulnerable people in the Middle East,” he said. “They badly need a U.N agency that will provide them with emergency and humanitarian services.”