NAIROBI, Kenya—The U.S. stepped up its harsh criticism of Kenya, raising again the threat of sanctions against a longtime east African ally that has become riddled with infighting and allegations of corruption.

"Nothing's off the table," said Karl Wycoff, the deputy assistant secretary of state for African Affairs, referring to steps Washington is willing to take as it urges Kenya to crack down on political violence and root out corruption.

Washington's hard line against Kenya began building after the disputed 2007 presidential elections sparked ethnic clashes that killed more than 1,300 people and displaced tens of thousands more. Rivals Mwai Kibaki and Raila Odinga agreed to a internationally brokered power-sharing deal that made them president and prime minister, respectively. They pledged to work together to end ethnic disputes and overhaul the country's colonial-holdover constitution.

Two years later, however, their coalition government reamains shaky and the country is on edge. The U.S. is increasingly impatient for the government to take steps to punish those responsible for the postelection violence, crack down on corruption and amend the constitution.

"We will not hesitate to give our opinions when we feel that's what needs to be done," Mr. Wycoff said. "We will take strong actions when we think that's what needs to be done to move the reform process forward."

NAIROBI, Kenya—The U.S. stepped up its harsh criticism of Kenya, raising again the threat of sanctions against a longtime east African ally that has become riddled with infighting and allegations of corruption.

"Nothing's off the table," said Karl Wycoff, the deputy assistant secretary of state for African Affairs, referring to steps Washington is willing to take as it urges Kenya to crack down on political violence and root out corruption.

Washington's hard line against Kenya began building after the disputed 2007 presidential elections sparked ethnic clashes that killed more than 1,300 people and displaced tens of thousands more. Rivals Mwai Kibaki and Raila Odinga agreed to a internationally brokered power-sharing deal that made them president and prime minister, respectively. They pledged to work together to end ethnic disputes and overhaul the country's colonial-holdover constitution.

Two years later, however, their coalition government reamains shaky and the country is on edge. The U.S. is increasingly impatient for the government to take steps to punish those responsible for the postelection violence, crack down on corruption and amend the constitution.

"We will not hesitate to give our opinions when we feel that's what needs to be done," Mr. Wycoff said. "We will take strong actions when we think that's what needs to be done to move the reform process forward."