MONROVIA (Reuters) - The U.S. embassy in Liberia on Wednesday defended the credibility of last month’s presidential election there, amid allegations of irregularities and fraud that have delayed a run-off poll.

First-round winner George Weah, a former international football star, was initially set to face the runner-up, Vice-President Joseph Boakai, last week to determine who will replace current term-limited President Ellen Johnson Sirleaf.

But the third-place finisher, Charles Brumskine, contested the outcome of the first round, claiming gross irregularities had occurred and accusing NEC officials of fraud, an allegation the body denies.

“No accredited Liberian, regional, or international observation group suggested that the cumulative anomalies observed reflect systemic issues sufficient to undermine the fundamental integrity of the electoral process,” the U.S. embassy said in a statement.

Liberia’s Supreme Court ordered the elections commission to fully examine Brumskine’s allegations last week, a decision likely to push back the run-off date by weeks and even creates the possibility of the first round being re-run.

A number of first-round candidates, including Boakai, have publicly backed Brumskine’s challenge to the results and echoed his fraud allegations.

The dispute led Johnson Sirleaf, a Nobel Peace Prize winner, to state in a radio address following the Supreme Court decision that Liberia’s democracy was “under threat”, without elaborating.

“Efforts by any actors to impede the expressed will of Liberia’s people for personal ambition could risk goodwill and future investments in Liberia by international partners,” the U.S. statement warned.

Liberia, Africa’s oldest modern republic, was founded by freed U.S. slaves in 1847, and maintains a special relationship with the United States.

The West African timber and rubber producer is still trying to heal the wounds of one of the continent’s most brutal civil wars, which ended nearly 15 years ago. A successful vote would be its first democratic transfer of power in more than seven decades.