The United States says it is "deeply concerned" about political developments in Sudan, where new laws have raised tensions between the northern-based government and semi-autonomous south.
The State Department said it was responding to reports that the north's ruling National Congress Party (NCP) broke an agreement with the south's dominant SPLM party and changed the language in a key bill.
The bill, setting terms for a referendum on southern independence, was passed Tuesday, despite a protest by southern lawmakers who walked out of parliament.
A State Department spokesman says the NCP's actions jeopardize implementation of the 2005 peace deal that ended Sudan's north-south civil war.
The U.S. says it is also deeply concerned a new law passed Sunday affirming powers of Sudan's National Security Service.
The U.S. says Sudan's government must show that the law will not be used to arrest and detain political opponents if elections set for April are to be credible.
Analysts have warned that tensions in Sudan are rising to dangerous levels as the elections draw near. Northern and southern leaders have accused each other of failing to carry out the 2005 peace deal, which ended a 21-year conflict.
Along with elections, the agreement calls for a 2011 vote on whether southern Sudan will secede from the rest of the country.
The law passed Tuesday allows southerners living in northern Sudan to cast absentee ballots in that vote. The south says the National Congress Party added that language in a last-minute amendment.
A day earlier, NCP leaders accused southern officials of inflating voter registration rolls for the April elections. The south says the rolls are accurate, and that earlier estimates of eligible voters were too low because of a faulty national census.
In its statement Wednesday, the United States called on all parties in Sudan to work together to ensure the coming elections and referendum are conducted in a credible manner.