Saudi Crown Prince Mohammed bin Salman's dramatic one-two punch against perceived rivals at home and abroad is sending shock waves through the royal family, fueling turmoil in global markets and underscoring the de-facto ruler's concerns about his grip on the oil-rich kingdom.

On Friday, Saudi authorities rounded up the brother and a nephew of Prince Mohammed's father, King Salman bin Abdulaziz, on the grounds they were plotting a coup, said a person familiar with the matter. The next day, the world's largest oil exporter slashed prices for its crude by the most in more than 30 years, triggering a price war with Russia that threatens to roil a world economy grappling with the coronavirus outbreak.

The prince has big plans to transform his country into a modern powerhouse, but he faces a rocky path as the outbreak pummels oil demand The arrests on treason allegations that could carry the death penalty — unprecedented against such senior relatives — suggest he's not going to let anything get in his way.

"So much of what happens under MBS's leadership is based on the element of surprise, of shifting balance, and claiming control," said Karen Young, a resident scholar at the conservative American Enterprise Institute in Washington. "But the biggest threat to Saudi right now is the possibility of very low oil prices, back to 2015 or lower levels. This the crown prince will find harder to control."

New information on Sunday from the New York Times on a connected arrest indicates that the scope of the roundup isn't known. The Wall Street Journal reported that dozens of Interior Ministry officials, senior army officers and others suspected of supporting a coup attempt were also detained. Authorities later began releasing some of those questioned in the clampdown, the Journal reported.

The arrests highlight a lingering climate of fear that has made foreign and local investors skittish, Young said. But it was already going to be a bad year in terms of economic outlook because of the global slowdown from the impact of the coronavirus and the effects on energy demand.

Brent crude tumbled by almost a third to $31 a barrel Monday as traders reacted to the Saudi price cuts. That followed the oil market's biggest drop in a decade on Friday.

Saudi authorities have yet to comment on the arrests.

The prince's efforts to cast himself as a reformer and ally of the West have run against the less-flattering reality of his ruthless consolidation of power and foreign policy adventures such as the war in Yemen and boycott of Qatar.

Three years ago he had hundreds of royals and senior businessmen rounded up on corruption allegations, locking them in the Ritz-Carlton hotel as part of a purge against perceived critics. A year later, Saudi agents killed and dismembered a prominent critic, Jamal Khashoggi, inside the Saudi consulate in Istanbul. Both shook confidence in the reform plans and effort to attract outside investment.

More recently Amazon.com boss Jeff Bezos alleged that Prince Mohammed personally hacked his phone — a claim denied by Saudi officials.

King Salman's support for his son appears to have not wavered even though ties with the West are under severe strain. President Donald Trump has also continued to back the crown prince.

Yet while many in the royal family, which numbers in the thousands, pledge loyalty to Prince Mohammed, his consolidation of power has marginalized or alienated others.

"If your position is good, you're having concerts, there's no pressure from your society, then your only opposition is from the highest level of your family," said Kamran Bokhari, director of analytical development at the Center for Global Policy in Washington.

The arrests underline Prince Mohammed's tactic of unbalancing domestic rivals ahead of his expected ascension to the throne. They come at a critical time as he tries to ease the fallout from his penchant for making enemies at home and abroad, and prepare for a year in the international spotlight under the Group of 20 chairmanship.

The move against people at the apex of the country's security signals that Prince Mohammed feels his position is very vulnerable, Bokhari said.