The chief of the US military said Sunday he favors closing the prison here as soon as possible because he believes negative publicity worldwide about treatment of terrorist suspects has been "pretty damaging" to the image of the United States. "I'd like to see it shut down," Adm. Mike Mullen said in an interview with three reporters who toured the detention center with him on his first visit since becoming chairman of the Joint Chiefs of Staff last October. His visit came two days after the sixth anniversary of the prison's opening in January 2002. He stressed that a closure decision was not his to make and that he understands there are numerous complex legal questions the administration believes would have to be settled first, such as where to move prisoners. The admiral also noted that some of Guantanamo Bay's prisoners are deemed high security threats. During a tour of Camp Six, which is a high-security facility holding about 100 prisoners, Mullen got a firsthand look at some of the cells; one prisoner glared at Mullen through his narrow cell window as U.S. officers explained to the Joint Chiefs chairman how they maintain almost-constant watch over each prisoner. Mullen, whose previous visit was in December 2005 as head of the U.S. Navy, noted that President Bush and Defense Secretary Robert Gates also have spoken publicly in favor of closing the prison. But Mullen said he is unaware of any active discussion in the administration about how to do it. "I'm not aware that there is any immediate consideration to closing Guantanamo Bay," Mullen said. Asked why he thinks Guantanamo Bay, commonly dubbed Gitmo, should be closed, and the prisoners perhaps moved to US soil, Mullen said, "More than anything else it's been the image - how Gitmo has become around the world, in terms of representing the United States." Critics have charged that detainees have been mistreated in some cases and that the legal conditions of their detentions are not consistent with the rule of law. "I believe that from the standpoint of how it reflects on us that it's been pretty damaging," Mullen said, speaking in a small boat that ferried him to and from the detention facilities across a glistening bay. He said he was encouraged to hear from U.S. officers here that the prison population has shrunk by about 100 over the past year, to 277. At one time the population exceeded 600. Hundreds have been returned to their home countries but U.S. officials say some are such serious security threats that they cannot be released for the foreseeable future. Only four are currently facing military trials after being formally charged with crimes. Mullen also walked through an almost-completed top-security courtroom where the military expects to hold trials beginning this spring for the 14 "high-value" terror suspects who had previously been held at secret CIA prisons abroad. He was told that audio of the proceedings might be piped to locations in the United States where families of the Sept. 11 terror attacks, and perhaps others, could hear them. Mullen's predecessor, retired Air Force Gen. Richard Myers, is a defendant in a lawsuit by four British men who allege they were systematically tortured throughout their two years of detention at this remote outpost. On Friday a federal appeals court in Washington ruled against the four men. It was six years ago that Guantanamo Bay received its first prisoners, suspected terrorists picked up on the battlefields of Afghanistan as the Taliban government was being ousted from power. The facility is on land leased from the Cuban government under terms of a long-term deal that predates the rule of President Fidel Castro. It is commanded by Navy Rear Adm. Mark Buzby. Gates, at a Dec. 21 news conference at the Pentagon, noted the administration's failure to settle the closure debate. "I think that the principal obstacle has been resolving a lot of the legal issues associated with closing Guantanamo and what you do with the prisoners when they come back (to the United States)," Gates said. "Because of some of these legal concerns - some of which are shared by people in both parties on Capitol Hill - there has not been much progress in this respect," he added. After the terrorist attacks of Sept. 11, 2001, the Bush administration considered Guantanamo Bay a suitable place to hold men suspected of links to the Taliban and al-Qaida, contending that U.S. laws do not apply there because Guantanamo is not part of the United States. Lawyers for the detainees have challenged that interpretation ever since. Before he finished his Guantanmo Bay visit and flew to Key West, Fla., Mullen got a look at a site on the eastern shore of Guantanamo Bay - opposite the terrorist detention center - where the US military is building a new refugee camp that would be used in the event of a sudden, major influx of refugees in the area. Initially the camp will be designed to hold 10,000 refugees and is scheduled to be finished by June.