An Alabama native who moved to Somalia to wage jihad alongside al-Shabab militants faces a Saturday deadline to surrender to the insurgents or be killed, according to his Internet posting.

Omar Hammami — whom the FBI named as one of its most-wanted terrorists in November — has engaged in a public fight with al-Shabab over the last year, and a Twitter account that terrorism analysts believe is run by Hammami or his associates announced Jan. 4 that al-Shabab fighters had given him 15 days to surrender, or else.

"Shabab make (an) announcement in front of amriki: drop ur weapon b4 15 days or be killed. Its on," the tweet from the Twitter handle (at)abumamerican said. Hammami's nom de guerre is Abu Mansoor Al-Amriki, or "the American."

The killing of an American foreign fighter would likely harm al-Shabab's efforts to recruit Westerners, but Hammami has felt in danger for many months. Hammami first expressed fear for his life in an extraordinary web video last March that publicized his rift with the al-Qaida-linked al-Shabab.

Hammami has since leveled a myriad of accusations at the group — corruption, murder, ignoring global jihad — and analysts agree the American has become an al-Shabab PR problem.

"Something tells me at some point they just need to shut this guy up. At some point he stops being a nuisance and starts being a problem," said Bill Roggio, editor of The Long War Journal. "He may be signing his own death warrant ... I suspect if they end up executing him they won't do it in the timeline that he claims."

Even if the death threat isn't carried out close to Saturday, Clint Watts — a former executive officer at West Point's Combatting Terrorism Center — said Hammami needs to flee if he wants to save his own skin.

"He's always going to be looking over his shoulder in Somalia. They're not going to forget and eventually they're going to come after him. I mean, he's just killing al-Shabab right now," said Watts, who suggested that Hammami must run, turn himself in to U.S. authorities or fight to stay alive in Somalia as long as he can.

"And I think he still ends up being killed in the long run," said Watts, a senior fellow at the Homeland Security Policy Institute and the Foreign Policy Research Institute.

Along with Adam Gadahn in Pakistan — a former Osama bin Laden spokesman — Hammami is one of the two most notorious Americans in jihad groups. Hammami has made frequent appearances in al-Shabab combat videos, and in 2011 he released two rap songs, "Send Me a Cruise (missile)" and "Make Jihad With Me." He's also released Islamic lectures.

That high-profile posture has led al-Shabab to label Hammami a narcissist. Or as Watts put it: "He's full of himself."

Hammami has grievances with al-Shabab that has angered the Somali fighters: First, that militant leaders live extravagant lifestyles with the taxes fighters collect from Somali residents. "War booty is eaten by the top dogs, but the guys who won it are jailed for touching it. A gun, bullets, some beans is their lot," abumamerican tweeted this month.

His second major grievance is that the Somali militant leaders sideline foreign militants inside al-Shabab and are concerned only about fighting in Somalia, not globally.

Hammami even claims that al-Shabab's leader — Mukhtar Abu Zubeyr, also known as Godane — sent al-Qaida's former East Africa chief — Fazul Abdullah Mohammed — to his death by directing Mohammed to a Somali government checkpoint in Mogadishu where he was shot and killed in June 2011. Mohammed, who had ties with Osama bin Laden, died one month after bin Laden was killed by U.S. Navy SEALs.

That theory may have credence to it. Roggio and Watts both say it's plausible that Fazul was set up, and a Kenyan government security official has told The Associated Press that Fazul was sent to his death. The official spoke only on condition he not be identified because he wasn't authorized to release that information.

Hammami also claims that al-Shabab assassinates fighters inside its group.

Al-Shabab slapped Hammami publicly in an Internet statement last month, saying his video releases are the result of personal grievances that stem from a "narcissistic pursuit of fame." The statement said al-Shabab was morally obligated to out his "obstinacy."

Aaron Zelin, a fellow at the Washington Institute for Near East Policy who runs the website jihadology.net, thinks Hammami's recent outbursts — on Twitter, and a short Arabic-language video — have been a way for the American to rally protective support for himself. Hammami has sought out al-Qaida central, the al-Qaida branch in Yemen and Islamic scholars to take his side, but he has largely been given the cold shoulder.

Watts said Hammami seems to indicate he is in a region of Somalia controlled by Mukhtar Robow, a rival al-Shabab leader of Godane's, so may have some clan protection there. But it's unclear if Robow would save the life of the American, Watts said.

Hammami has been seen in videos among al-Shabab's leaders, but he was passed over for a promotion and sidelined within the movement, Roggio said.

Hammami grew up in Daphne, Alabama, a bedroom community of 20,000 outside Mobile. The son of a Christian mother and a Syrian-born Muslim father, Hammami once served as the president of the Muslim Student Associated at the University of South Alabama. He moved to Somalia in 2005 or 2006.