State of emergency
Bangladesh has been under a state of emergency since January 11, imposed in the wake of deadly violence between supporters of former prime ministers Begum Khaleda Zia and Sheikh Hasina.
An election planned for January 22 was cancelled and all political activity banned.
The senators said: "We are troubled that the indoor ban on political activity was not lifted, as planned, on May 8.
"Moreover, we are concerned by the lack of progress towards free and fair elections in Bangladesh."
Ahmed has said he hopes to hold an election before the end of 2008, while the Election Commission said it would not be rushed by what other nations were saying.
Khaleda's Bangladesh Nationalist party (BNP) and Hasina's Awami league are also demanding an early election and the immediate lifting of the ban on indoor political activity.
The US senators lauded the efforts of the government to address corruption, saying that it was "critically important that any anti-corruption campaign be implemented in conjunction with Bangladeshi law and international standards".
Security forces have detained more than 160 key political figures including Khaleda's elder son and political heir apparent, Tareque Rahman, in an anti-corruption drive.
Khaleda's younger son Arafat Rahman also faces charges of extortion filed by a businessman on Wednesday, police said.
Hasina is facing charges of extortion and murders linked to political violence in Dhaka last October, weeks after Khaleda ended her five-year term as prime minister.