ALGIERS, Algeria — Heads have been rolling in the Algerian army, the North African nation's most respected institution, and in other security services, with generals in top posts fired — without explanation — at a rate never before seen.

The across-the-board changes, and the silence, are highlighting the opaque nature of the nation's power structure.

Since late June, nearly all top officials in the security hierarchy have been replaced. The changes are especially dramatic in a country with the best-equipped military in North Africa and the Sahel that has honed for more than a quarter-century its skills in fighting Islamic extremists. Today, Algeria is a bulwark against extremism for the West.

Yet the noisy Algerian press, which habitually decodes the often inscrutable world of politics, has been unable to decipher the reason for the massive clearout.

Is a scandal surrounding a huge cocaine seizure the reason for at least some of the firings, or is it a about traditional rivalries among powerful clans? Or are the changes connected to next April's presidential elections, which is the subject of another mystery — who is running? No candidate has yet emerged because everyone is waiting to learn whether President Abdelaziz Bouteflika, 81, partially paralyzed and rarely seen in public, will seek a fifth term.

Such changes in the military hierarchy, only some of which have been announced publicly, are the prerogative of the president, who is also minister of defense. But the influence of the army is a perennial mystery.

The wave of changes began with the firing June 26 of Gen. Abdelghani Hamel, head of the General Directorate of National Security, the top echelon of Algeria's police. Along with Hamel went the men he had placed in more than a half-dozen top regional police posts, from Algiers, the capital, to Setif, in the east — as well as the commander in charge of Algiers' international airport.

The most recent to be axed were the Air Force commander and the head of the Air Defense Force, announced last week by the Defense Ministry.

The ousting of Hamel, who had held the top police post since 2010, may — or may not — be linked to the May seizure by the Coast Guard in the port of Oran of 701 kilograms of cocaine hidden among frozen meat on a cargo ship from Brazil, and his harsh words directed to the gendarmerie investigating the affair. However, eight days after Hamel's ouster, it was the gendarmerie chief, Maj. Gen. Menad Nouba, who lost his job.

The sword then fell on the top brass of the army, the backbone of the Algerian state. Region by region, top leaders were removed. Only one of the six military regions has been left untouched.

"No one is indispensable," said political sociologist Nasser Djabi, "even the all-powerful." He recalled the removal in 2015 of one of Algeria's most powerful figures, intelligence chief Gen. Mediene, known as Toufik, after 25 years on the job. "If you ask me who profited from these changes, what is the balance of power ... I'm unable to say. It's very opaque."

Ahmed Gaid Salah, army chief of staff since 2004 and vice-defense minister, and among Bouteflika's most faithful servants, has overseen ceremonial changeovers in the regional commands, at one point saying they were dictated by "competence" and "merit."

In a fuller explanation, the army review El Djeich said last week the new appointments "embody the principle of alternating posts of responsibility" and "are an opportunity to encourage human capacities, reward experience and push (new chiefs) to redouble their efforts in the service of our army."

The army, which grew out of the fighting force that won Algeria's independence from France in 1962, was long seen as the kingmaker in presidential elections. Only Bouteflika — in office since 1999 — and the country's short-lived first elected head of state have been civilians.

However, army chief Gaid Salah cast aside in July any notion of an army role in politics, brusquely responding to a proposal by an opposition party for the army to head a transition period and delay presidential elections.

"The National Popular Army is an army that knows its limits, the framework of its constitutional mission that in no case can be mixed up in entanglements in parties and politics," he said.