Hailemariam Desalegn was named acting head of government this week after longtime leader Meles Zenawi died Monday at the age of 57.
Ethiopians are still awaiting word on when Hailemariam will be formally sworn in. Parliament was set to install him on Wednesday but the session was canceled.
A government spokesman said Ethiopians wanted more time to mourn Meles, who led Ethiopia for 21 years. The late prime minister's funeral is scheduled for September 2.
U.S. President Barack Obama spoke by phone with Hailemariam late Thursday. The White House says Obama pledged continued U.S. partnership with Ethiopia, and urged the acting prime minister to - in the words of a statement - "enhance the Ethiopian government's support for development, democracy, human rights and regional security."
Under Meles, Ethiopia has been a strong ally in the U.S. war against terrorism, but was criticized for oppressing the media and political opponents.
On Tuesday, Communications Minister Bereket Simon rejected concerns about a power vacuum resulting from Meles' death. He says the country's leadership is united and the government is as "strong as ever."
Hailemariam had served as Meles' deputy since 2010.