Cairo - Egypt and Saudi Arabia have long been key allies but tensions over regional issues including Syria and Yemen have erupted into the open in rare public disagreements.
The discord came to the surface when Egypt on Saturday voted in favour of a Russian-drafted UN Security Council resolution on Syria strongly opposed by Riyadh.
That was followed by Cairo's announcement of Saudi oil giant Aramco's surprise decision to halt the expected delivery of 700 000 tons of petroleum products to Egypt this month, forcing Egypt to rush out a call for tenders to make up the shortfall.
Analysts say the row - which threatens to distance Egypt's President Abdel Fattah al-Sisi from one of his main backers - reflects longstanding disagreements on crucial regional issues.
"There is always talk that there is a strategic alliance between Cairo and Riyadh, and that is not true," prominent Egyptian journalist and commentator Abdallah el-Sennawy said.
"A strategic alliance means an understanding on regional issues, which is something that does not exist in the Syrian and Yemeni files. The discord now has exploded and risen to the surface."
Sisi has relied on Saudi support since the then army chief overthrew Islamist president Mohamed Morsi in 2013, with Riyadh since providing billions of dollars in aid and credit.
Saudi King Salman visited Cairo on a rare trip abroad in April, hailing Sisi and approving a slew of investment deals.
Even then, however, there were reports of Saudi frustration over Cairo's reported reluctance to fully back Riyadh's regional ambitions, in particular in its rivalry with Iran.
Sunni-ruled Saudi Arabia and Shiite-dominated Iran are opposed in a range of regional conflicts and disputes, in particular the wars in Syria and Yemen.
Cairo "does not see the threat of the Iranians" in the same way as Riyadh, said Saudi journalist and analyst Jamal Khashoggi.
"Saudi Arabia tolerated the Egyptian position over and over again, and I think what happened at the UN vote is the straw that broke the camel's back," Khashoggi said.
Saudi bitterness at Cairo's vote was clear when Riyadh's envoy to the UN Abdullah al-Muallimi told Al-Jazeera: "It was painful for the Senegalese and Malaysian positions to be closer to the Arab consensus than that of the Arab representative."
In Syria, the Saudis fiercely oppose the Iran-backed government of President Bashar al-Assad and have provided crucial support to armed opposition factions.
Egypt has been more cautious, saying Assad should be part of efforts to find a political solution to the country's five-year-old civil war.
"Saudi Arabia's position is final about Assad's departure and (Riyadh) sees it as a solution for the crisis, while Egypt stands with a political solution... with Assad being one of its elements," said Amin Shalaby, executive director of the Egyptian Council for Foreign Affairs, an independent think tank in Cairo.
In Yemen, Saudi Arabia has been leading an Arab coalition since last year backing pro-government forces against Iran-supported Shiite Huthi rebels who have seized control of much of the country, including the capital Sanaa.
On paper, Cairo has committed troops to join the coalition forces in Yemen if needed. But analysts say that behind the scenes, Egypt has been reluctant to engage.
"Egypt avoided being implicated because of the traumatic experience in the 1960s," Sennawy said, referring to ex-president Gamal Abdel Nasser's sending of tens of thousands of troops to Yemen in support of a 1962 republican coup against the then-monarchy.
Egyptian troops were trapped in a years-long quagmire in Yemen, with some historians referring to the conflict as "Egypt's Vietnam".
The growing dispute could have real and immediate consequences for Egypt, analysts say.
Aramco's surprise decision to suspend petroleum product exports to Egypt applies only to October, so far.
Egypt, the most populous Arab nation, needs some 6.5 million tons of petroleum products to meet its monthly domestic needs, with imports - 40% of them from Saudi Arabia - accounting for 1.75 million tonnes.
Egyptian economist Ibrahim al-Ghitani said "political issues" were clearly behind the decision.
"I don't think there are any technical problems in the Saudi company. And we haven't heard of any similar situation from Aramco towards other countries," Ghitani said.
Still, analysts say Saudi Arabia is unlikely to turn the screws too tight on its ally, which has faced a series of economic crises since the 2011 uprising that toppled longtime president Hosni Mubarak.
"It (Saudi Arabia) worries that things are not going very well in Egypt and it doesn't want to add more pressure on the Egyptian government," Khashoggi said.
"Things are not going well economically, (there is) political stagnation, so there is a recipe for another crisis in Egypt," he said. "And no one needs one more crisis in the region."