Barack Obama faces an uncertain reception today when he visits America's largest military base to pay his respects in a memorial service for 13 people killed in a shooting rampage last week.

The President has come under criticism for misreading the public mood in his first statement after the shootings in Fort Hood, Texas, last Thursday, and his critics in the armed forces say that he has yet to prove himself as Commander-in-Chief.

He has also to show that he can perform that other presidential role: as healer-in-chief after a national tragedy that has polarised opinion because the alleged gunman, Major Nidal Malik Hasan, is a Muslim who had fought a long campaign to be released from the US military to avoid deployment in Afghanistan or Iraq.

Mr Obama and his wife, Michelle, were due to spend about four hours on post at Fort Hood meeting the families of those killed, before a memorial service that is sure to be watched by American troops around the world. The President and First Lady will also visit wounded troops ina local hospital before returning to Washington.

Meanwhile, questions were increasingly being asked about the Fort Hood gunman's links to an imam with connections to at least two of the 9/11 hijackers.

The FBI said Major Hasan, a military psychiatrist, came to its attention last year after he communicated with Anwar al-Aulaqi, who was then the target of an FBI terror investigation.

The FBI said investigators assessed that the alleged gunman’s communications with the suspect were“consistent with research being conducted by Major Hasan in his position as a psychiatrist at the Walter Reed Medical Centre in Washington.

“Because the content of the communications was explainable by his research and nothing else derogatory was found, the JTTF (joint terrorism task force) concluded that Major Hasan was not involved in terrorist activities or terrorist planning,” it said.

The FBI added that “the investigation to date indicates that the alleged gunman acted alone and was not part of a broader terrorist plot".

Mr Hasan has been able to talk for the first time since opening fire on his he allegedly opened fire on fellow soldiers until he was hit by a female police officer, although he has so far refused to talk to investigators.

“He is talking. He is conversing with the medical staff,” said a spokeswoman for the Brooke Army Medical Center in San Antonio.

In a television interview on the eve of his visit to the base, Mr Obama said the question was whether Hasan acted alone. “Is this an individual who’s acting in this way, or is it some larger set of actors?" he asked.

Senator Joseph Lieberman, who chairs the Senate Homeland Security Committee, said he would launch a probe into whether the army missed any warning signs which could have prevented the attack.

While investigators believe that 39-year-old Hasan acted alone, he appears to have telegraphed his actions. The Washington Post reported that Major Hasan warned a roomful of senior army physicians a year and a half ago that to avoid “adverse events” the military should allow Muslim soldiers to be released from duty as conscientious objectors.

“It’s getting harder and harder for Muslims in the service to morally justify being in a military that seems constantly engaged against fellow Muslims,” he was quoted as saying in the investigation.

The FBI Director Robert Mueller, after meeting with Obama, ordered a full review of the shooting incident with the aim of determining whether “with the benefit of hindsight, any policies or practices should change based on what we learn”.

Mr Obama told ABC television that he was determined “to complete this investigation and we are going to take whatever steps are necessary to make sure that something like this doesn’t happen again".

Robert Gates, the US Defense Secretary, visited the base yesterday to meet the families of those killed and to visit some of the wounded, including police sergeant Kimberly Munley, hailed as a heroine for confronting the gunman.

The bloody spree left army officials still scrambling to understand how one of their own could turn on his fellow soldiers. Officers must now keep an eye out for similar signs of disquiet “across our entire formation, not just in the medical community, but look hard to our right and left,” said Lieutenant-General Robert Cone, the Fort Hood commander.

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