The council imposed the embargo in 2001, two years before the end of Liberia's 14-year diamond-fueled civil war.
The resolution also asked a panel of four outside experts to continue to monitor the government's progress and report back to the council by June 6 on whether the diamond embargo could be lifted at that time.
Liberia demands end to embargo
Ellen Johnson-Sirleaf, the Liberian president, who took office last January, has pushed hard for an end to the embargo. She says that the money from diamond sales was badly needed to finance reconstruction in her war-ravaged West African country.
But the expert panel told the security council that Liberia had not yet met the requirements of the Kimberley Process, a mechanism that requires participating governments to provide certificates for exports of rough diamonds to show they were mined from legitimate operations.
The voluntary initiative between governments and the diamond industry was launched in 2002 to end the use of rough diamonds to finance wars, as occured in Angola, Ivory Coast, the Democratic Republic of Congo and Sierra Leone.
The expert panel said Liberia had made progress toward fulfilling the Kimberley Process requirements but still needed to ensure its efforts led to "a coherent and functioning mechanism with long-term durability and credibility."
But the UN said the country still faced enormous reconstruction challenges and said the government failed to tackle corruption.