The Gulf state blew past a Sunday deadline to meet a series of demand that from Saudi Arabia and its allies that Doha describes as an "affront to international law."
World health authorities say the war-torn nation now has upwards of 200,000 suspected cases, and that number is increasing at an average of 5,000 a day. A quarter of those who have died are children.
If Qatar wants to end a recent diplomatic standoff, Saudi Arabia and three other Arab states say the country has 10 days to comply with a steep list of demands, including shutting down Al-Jazeera.
Mohammed bin Salman is now first in line to the throne. At 31, he has already reshaped his country's role in the region. His biggest test will come as he tries to wean the kingdom off an oil economy.
Saudi Arabia's new successor to the throne is 50 years younger than the current monarch. He's known for his social and economic views, as well as leading the Saudi military.
It's the most recent flare-up in a series of long-running tensions between Qatar and Saudi Arabia and the Gulf states. This time, analysts say, there will be no easy or quick resolution.
Ahead of a World Cup qualifying match, the Australian players lined up in a row and stood silently in memory of the eight people killed. Members of the Saudi team did not.
At least 17 people have died in Wednesday's twin terrorist attacks. President Trump expressed condolences but said "states that sponsor terrorism risk falling victim to the evil they promote."
After tweets that seemed to side against Qatar, President Trump has offered to host a meeting to work out problems between the small oil-rich nation and its neighbors, which are seeking to isolate it.
The White House and the State Department stressed the need for cooperation among Arab allies, after President Trump appeared to take the side of Saudi Arabia and its Gulf neighbors against Qatar.