“Hamas is tightening the grip on our necks and storms our houses,” a Salafist said in an interview this week at his house in a refugee camp in central Gaza. Speaking on the condition of anonymity to avoid the attention of the Hamas authorities, he added, “We are chased down by Israel, Hamas and Egypt.”

The activist used to belong to another radical group called Jund Ansar Allah, or Soldiers of the Supporters of God, which was crushed by Hamas in 2009. Now, he spends most of his time researching Islamic law and consulting with other Salafists who come to his home, which has a library of about 100 books on Islamic subjects.

A Salafist leader who also spoke anonymously for fear of reprisal by Hamas said in an interview, “The jihadists as groups are over now.” He said Hamas had been going after the groups one by one.

Hamas government officials refused to comment on measures against the Salafist militants. But Yahiya Moussa, a Hamas member of the Palestinian Parliament, said that while the Salafist groups had the right to carry out resistance against Israel, it must be “within the unified and national program,” meaning in line with Hamas policy.

A senior Israeli defense official, Yossi Kuperwasser, said that in Gaza, Israel was facing a “hostile governing element challenged by an even more hostile element” and that “radical Islamic groups are competing with each other over who is more radical.” In a briefing with reporters in Jerusalem this week, Mr. Kuperwasser, the director of Israel’s Ministry of Strategic Affairs, also said the Palestinian Islamic Jihad group, another significant force positioned somewhere between Hamas and the Salafists, was becoming stronger and better armed. Twice this month, Israel has launched deadly missile strikes against militants in Gaza whom it identified as operatives in the global jihad movement, saying they were involved in firing rockets and planning other attacks against Israel.