The Nov. 8 elections are widely viewed in the West as a key measure of Myanmar's internal reform. They will be the country's first general elections since a nominally civilian government was introduced in 2011 after nearly 50 years of military rule and diplomatic isolation.
The Obama administration moved to normalize ties after the new government took major steps toward reform, including releasing political prisoners, allowing an independent press and permitting political parties.
The diplomatic opening to Myanmar was considered one of the top foreign policy achievements of President Obama's first term. It also was viewed as a personal success for then-Secretary of State Hillary Rodham Clinton, who is now running for president.
But the government in Myanmar, also known as Burma, has appeared to embrace more autocratic practices again in the last few years.
Critics have accused the government of moving too slowly to share power with political rivals, and of mistreating ethnic minorities, especially a Muslim group known as the Rohingya.
In a statement, Kirby noted reports that almost all Muslim candidates have been disqualified for the parliamentary elections.
He said authorities "have yet to provide the specific reasons for which they did not meet these criteria."
"We urge the Burmese authorities to redouble their efforts to address these concerns and ensure that the upcoming elections constitute a step forward for the country," he said.
Reform advocates contend that if the elections are free and fair, they will sweep into office a large number of pro-reform lawmakers.
They contend that the government's exclusion of Muslims is aimed at building support from the country's extreme nationalist and anti-Muslim parties.
Simon Billenness, of the advocacy group U.S. Campaign for Burma, urged the Obama administration to increase pressure on the government by imposing sanctions on some of its members.
The administration has been "willing to speak out, but not willing to use their leverage by adding people to the sanctions list," he said.