CAIRO — Egypt’s prime minister surprised members of his cabinet on Monday by abruptly announcing the resignation of the military-backed government, which had struggled to manage the country over seven months of political unrest and growing criticism of its performance.

The prime minister, Hazem el-Beblawi, who was appointed last July soon after the military ousted the country’s Islamist president, Mohamed Morsi, did not give any reasons for the decision or explain its timing. Quickly, though, there was speculation that it was somehow intended to clear the way for Field Marshal Abdul-Fattah el-Sisi, the defense minister and the dominant figure in the government, to announce his candidacy in the coming presidential election.

Yet like many of the decisions emanating from Egypt’s top echelons these days, Mr. Beblawi’s precise motives remained opaque — even to members of his own government. One minister said he was called into a meeting on Monday after the regular Tuesday cabinet meeting was rescheduled.

“I walked in this morning,” he said. “The resignation statement was read. I left.” Mr. Beblawi “didn’t talk about the reasons,” he said.