WASHINGTON - US Attorney General Eric Holder is considering alternative sites to New York City for prosecuting the accused plotters of the Sept. 11 attacks amid rising pressure and concerns about security and costs, an administration official said on Friday. The Obama administration has been harshly criticized for plans to try Khalid Sheikh Mohammed and four of his alleged co-conspirators a few blocks from where the World Trade Center twin towers stood because of worries about a large security cordon and the potential impact on businesses in the area. Holder, who picked New York City in November for the trials, is considering alternative venues than the Manhattan courthouse, one administration official said. "Conversations have occurred with the administration to discuss contingency options should the possibility of a trial in lower Manhattan be foreclosed upon by Congress or locally," a second administration official said. It was not clear what other venues would be considered. New York officials have suggested options like a military base, the US Military Academy at West Point, New York, or nearby Governor's Island, though some said that last option was not feasible. Further, one US official has said that no terrorism trials had been held outside of a federal courthouse and there are questions whether a trial could be held on a military base. The decision to reconsider comes after intense bipartisan pressure and poses another hurdle for President Barack Obama who has been trying to focus on passing his health insurance reform initiative and reducing the high unemployment rate. Earlier this week, New York City Mayor Michael Bloomberg reversed his support for holding the trials in the heart of Manhattan and he was quickly joined in his opposition by others. "I can tell you I would prefer if it was done elsewhere, I think some of the suggestions make sense, like a military base, because it's far away from people and you can provide security easily," Bloomberg said on Friday on his weekly radio show. He said he called the administration on Thursday to express his concerns and acknowledged that ultimately the city could handle the trials. "I will be as supportive as, and the city will be, as supportive as we can, period," Bloomberg said. He has estimated the cost of security for the trial to be at least $200 million a year and has asked the Obama administration to pick up the tab. That could be tough for Obama because he has had enormous trouble getting the US Congress -- despite a sizable Democratic majority in the Senate and the House of Representatives -- to approve money for his bid to close the US prison at Guantanamo Bay, Cuba, that holds terrorism suspects. Republicans and even some of President Barack Obama's fellow Democrats have ramped up pressure in recent weeks against the planned criminal trials, urging that the alleged Sept. 11 plotters be tried in military tribunals instead.