The executions come as a Saudi-led military campaign intensifies in neighbouring Yemen and Crown Prince Mohammed bin Salman, the kingdom's de facto ruler, consolidates his grip on power.

The soldiers were convicted of "the crime of high treason in cooperation with the enemy" in a way that threatens the kingdom and its military interests, the ministry said in a statement carried by the official Saudi Press Agency.

The statement named the three soldiers -- Mohammed bin Ahmed, Shaher bin Issa and Hamoud bin Ibrahim -- without identifying which enemy they were accused of aiding.

The ministry said the soldiers were executed in the military's Southern Command, based close to the border with Yemen, where Saudi Arabia is leading a six-year campaign against Huthi rebels.

Saudi Arabia, a Sunni powerhouse, views Shiite Iran as its main regional foe and identifies the Tehran-aligned Huthis as a major security threat to the oil-rich kingdom.

Riyadh led a military coalition into Yemen in March 2015 to prop up the internationally recognised government, but it has struggled to oust the Huthis.

It has also faced a surge in missile and drone attacks against the kingdom.

Fighting has intensified for the key Yemeni region of Marib, with 53 pro-government and Huthi rebel fighters dead in the past 24 hours, loyalist military officials said Saturday.

The Huthis have been trying to seize oil-rich Marib, the government's last significant pocket of territory in the north, since February.

- Consolidating power -

The executions come as Prince Mohammed, the 35-year-old heir to the throne, tightens his control on power.

Prince Mohammed -- the son of King Salman, the kingdom's ageing monarch -- is already viewed as the country's day-to-day ruler, controlling all the major levers of government, from defence to the economy.

He holds the title of defence minister, while his younger brother Prince Khalid bin Salman is the deputy.

Over the past three years, the crown prince has mounted a sweeping crackdown on critics and rivals, with the imprisonment of prominent royal family members, business tycoons, clerics and activists.

In March last year, Prince Ahmed bin Abdulaziz al-Saud, a brother of King Salman, and the monarch's nephew Prince Mohammed bin Nayef were detained, multiple sources said, as the crown prince sought to stamp out traces of internal dissent.

Saudi authorities have not publicly commented on their ongoing detention.

The kingdom has long faced criticism for one of the world's highest rates of executions and what human rights campaigners call an opaque judicial system.

But earlier this year, the government-backed Human Rights Commission (HRC) reported a sharp drop in executions in 2020, as the kingdom seeks to blunt international criticism of its human rights record.

The HRC said it documented 27 executions in 2020, a decrease of 85 percent over the previous year due in part to a moratorium on the death penalty for drug-related offences.