U.S. Deputy Secretary of State Bill Burns listens to a speaker during the Friends of Yemen ministerial meeting in central London, March 7, 2013. (AFP/Getty Images)

The second-most senior U.S. diplomat has met with the imprisoned deputy leader of the Muslim Brotherhood, according to a senior official, a sign that the United States is ramping up its attempts to mediate Egypt's political crisis.

U.S. Deputy Secretary of State Bill Burns traveled late Sunday night to the notorious Tora Prison, a jail in the middle of Cairo that has housed some of Egypt's most famous prisoners, to meet with Khairat el-Shater, the official said.

The Brotherhood had claimed until now that El-Shater refused to meet.

Egypt's First Democratically Elected President Ousted

El-Shater, one of the country's wealthiest businessmen, is highly influential within the Brotherhood and the organization's main financial backer. After the military overthrew the government last month, el-Shater was detained along with hundreds of Brotherhood supporters as part of the military's crackdown on the Islamist group.

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