A Palestinian leader jailed by Israel is urging Palestinians at home and abroad to stage mass rallies in September to support a bid to gain U.N. membership for an independent Palestine.

In a letter published Wednesday in Palestinian media, Marwan Barghouti calls for “millions” of Palestinians to demonstrate peacefully in Palestinian communities, Arab and Muslim nations and international capitals.

Barghouti is a popular leading member of the Fatah movement of Palestinian President Mahmoud Abbas. Israel jailed Barghouti for life in 2004 on charges of murder related to the killings of Israelis in a Palestinian uprising a decade ago.

In the letter, Barghouti says Mr. Abbas' bid for U.N. membership is an “important milestone” in the Palestinian struggle for independence. But, he says Palestinian diplomatic efforts will not be enough to achieve freedom unless Palestinians also engage in “struggle and resistance on the ground.”

Israeli officials have expressed concern that the Palestinians' U.N. bid could trigger anti-Israel unrest inspired by uprisings in the Arab world.

Israel and its chief ally the United States have said the borders of a future Palestinian state must be determined by negotiations. Both nations oppose Mr. Abbas' U.N. bid.