The decision by Oman came first as the neighboring United Arab Emirates initially just said it had joined U.S. authorities and Boeing Co. "to investigate and collect data" to help solve what happened in Sunday's crash in Ethiopia that killed all 157 people on board. Late Tuesday, it announced Boeing 737 MAX 8 and 9 aircraft had been grounded.
Oman's Public Authority for Civil Aviation made the sultanate's announcement, without elaborating on its reasoning.
The state-owned Oman Air, which operates five Boeing 737 MAX 8 aircraft, said flights operated by those planes "will be suspended as soon as possible."
"We are in the process of making the necessary rescheduling and will advise our guests of any flight cancellations," the airline said.
Oman, ruled by Sultan Qaboos bin Said for nearly 40 years, sits on the eastern edge of the Arabian Peninsula.
Since the crash Sunday, regulators across the world have begun grounding the aircraft as an investigation into the disaster's cause continues.
The 737 MAX is the workhorse of the Dubai government-owned budget carrier FlyDubai. It operates 11 Boeing 737 MAX 8 and 2 MAX 9 jetliners. Its total fleet is around 60 aircraft, including other models of the 737.
Earlier on Tuesday, FlyDubai said that "no further action is required at this time" over the aircraft. After the Emirates banned the aircraft, the airline said it would be "adjusting its schedule to minimize disruption to passengers."