A Republican congresswoman froze a request by the Obama administration for $450 million in cash for the Egyptian government, saying it needed new scrutiny amid rocky US ties with Cairo.
The lawmaker, Kay Granger, from Texas, who chairs the Appropriations Subcommitee on State and Foreign Relations, on Friday put a "hold" on the application, meaning it could be held up indefinitely.
"This proposal comes to Congress at a point when the US-Egypt relationship has never been under more scrutiny, and rightly so," Granger said in a statement.
"I am not convinced of the urgent need for this assistance and I cannot support it at this time. As Chair of the Subcommittee, I have placed a hold on these funds."
The purpose of the funds could not be immediately confirmed.
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But an official said the money, requested Friday, was part of a package worth $1 billion that Obama pledged to Cairo last year to aid its transition to democracy following its Arab Spring revolution.
The New York Times reported that the emergency cash infusion was requested by the US Agency for International Development because the economic situation in Egypt was causing increasing alarm.
Earlier this month, US President Barack Obama sparked intrigue over the state of US ties with Egypt after he said the country, in the post-Hosni Mubarak era, was neither a friend nor a foe.
But Egypt remains a non-NATO ally of the United States, allowing it to enjoy a close relationship with the US military, along with other allies including Australia, Japan, Jordan, Israel and Thailand.
Obama's comments came after a mob raided the US embassy in Cairo in protest at a film made on US soil and deemed anti-Muslim, which also caused riots across the Muslim world.
Washington appears to be still calibrating its likely future relations with the Muslim Brotherhood-led government of President Mohamed Morsi.