PKR communications director Fahmi Fadzil said the report of the British newspaper the Daily Mail was "wild allegations" and the paper "is a sensationalist tabloid known for cooking up stories."
"If there is any concrete data backing up an allegation we will respond to it. If anyone aboard (the flight) chose to attend the Anwar trial that is their right as it was in open court," he told the local English newspaper the Star.
The Daily Mail report claimed that Zaharie commanded the doomed flight about several hours after he had attended the sodomy trial of opposition leader Anwar Ibrahim on Friday.
Anwar was jailed for five years by the Court of Appeal last Friday but was released on bail. Flight MH370 with 239 passengers and crew on board took off from Kuala Lumpur International Airport (KLIA) at 12:40 a.m. on Saturday.
Asked if Zaharie was often seen at functions organized by PKR or the opposition alliance Pakatan Rakyat (Peoples Alliance), he said he does not know Zaharie personally.
"I did not know who he was until the news broke out about the plane last Saturday," said Fahmi.
PKR vice-president N. Surendran said there "is not a drop of evidence to support such speculation. It is just a speculation. Let us be fair to the missing captain as well -- he cannot answer for himself."