BEIRUT — When the Hamas rulers of Gaza recently gave a hero’s welcome to the ruler of Qatar, an arch foe of the Syrian regime, it sent a strong message reverberating across the capitals in Tehran, Damascus and Beirut.

The powerful, anti-American alliance of Iran, Syria and militant groups Hezbollah and Hamas, once dubbed the “Axis of Resistance,” is fraying.

Iran’s economy is showing signs of distress from nuclear sanctions, Syria’s president is fighting for his survival and Hezbollah in Lebanon is under fire by opponents who blame it for the assassination of an anti-Syrian intelligence official. Hamas — the Palestinian arm — has bolted.

“We’re seeing basically the resistance axis becoming much more vulnerable and under duress. So even if it survives, it’s really under tremendous pressure,” said Fawaz Gerges, director of the Middle East Center at the London School of Economics.

“The Hamas shift to the Saudi-Qatari-Turkish orbit represents a major nail in the coffin of the resistance axis,” he said. “Now you are talking about Iran and Syria and to a lesser extent Iraq and this undermines the social element because Hamas added the very important Sunni dimension.”

The axis is one of two powerful camps that divide the Middle East into spheres of competing influence. It faces off against the wealthy, powerful monarchies of Saudi Arabia and Qatar allied loosely with most of the other Arab countries and neighboring Turkey, which like Iran is Muslim but not Arab.

The fault line is sharply sectarian — Iran and Hezbollah are Shiite and Assad’s regime is dominated by the Alawite sect, an offshoot of Shiite Islam. Hamas, which is Sunni, had been the exception before it strayed. Qatar, Saudi Arabia and other Sunni Muslim-led Arab countries in the Gulf have been trying to stem the regional influence of Iran.

Also, the Sunni countries, along with Turkey, support the Sunni-dominated opposition waging the civil war against Assad’s rule in Syria.