WASHINGTON (Reuters) - U.S. officials voiced concern on Tuesday that Bahrain's failure to implement key reforms outlined in an independent 2011 report is making political dialogue more difficult and widening fissures in society in ways that would benefit Iran.

Bahrain, where the U.S. Fifth Fleet is based, has been under Western pressure to implement recommendations for police, judicial, media and education reforms made by the Bahrain Independent Commission of Inquiry (BICI), an independent commission of international legal experts.

"We are worried that this society is moving apart rather than coming together in a way that would ensure both human rights and stability," said a senior U.S. official, speaking to reporters on condition he not be identified by name.

"It's absolutely clear that if society breaks apart, Iran will be the big winner and beneficiary," added the official.

Shi'ite protesters complain they continue to be marginalized by Bahrain's Sunni rulers. The strategically located island state is a key U.S. ally in Washington's stand-off with Shi'ite Iran.

The BICI report, issued last year, said 35 people died during unrest which erupted in the Persian Gulf monarchy in February 2011 after revolts overthrew dictators in Egypt and Tunisia.

The U.S. official said Bahrain had "followed a number of the recommendations" including allowing Red Cross access to prisoners, issuing arrest protocols and modest police training and setting up an ombudsman in the Ministry of Interior.

"On the hardest issues, the government has not followed through," he said, citing people still being held in prison or facing prosecution for the early 2011 demonstrations.

"We remain concerned about increasing violence in Bahrain, by limits on free expression and assembly and a political environment that's become increasingly difficult and that's made reconciliation and political dialogue more difficult," said the official.

Washington also lamented fresh violence in the past month, including Molotov cocktails and other violent actions by protesters, as well an "excessive use of force by police and security forces," said the official.

A second U.S. official said the 60-year-old U.S. security relationship with Bahrain was critical to regional stability and required a balancing act by Washington.

American policy aimed to "balance those requirements and those interests with those we have at the same time in encouraging reform, given our commitment to the fact that reform is the only way we can see that genuine stability and prosperity will emerge in the region," said he second official.

(Reporting By Paul Eckert; Editing by Todd Eastham)