MH17 Lim Kit Siang and Anwar Ibrahim have heaped praises on Prime Minister Najib Abdul Razak in the handling of the MH17 crisis and brokering the handover of the two black boxes.
Also commending Najib was former Malaysian Bar Council president Ambiga Sreenevasan.
Lim said Najib must be commended for the breakthrough on the two black boxes.
"Malaysians must remain united on the MH17 disaster, continue to give full backing to Najib and the government to demand swift justice against the perpetrators of this crime against humanity in the murder of 298 passengers and crew on board in cold blood on July 17, 2014.
"For four days, there was international outrage over the heinous and senseless crime against humanity by the show of gruesome and insensitive disrespect to the remains of the MH17 victims, as well as the looting and contamination of the crash site," Lim said, noting that 80 of the passengers were children.
The Gelang Patah MP called for a full, independent and credible international investigation.
He also hoped that the United Nations Security Council's unanimous resolution last night demanding investigators to be given immediate access to the crash site and calling a ceasefire in the area, would be heeded by all three parties - Ukraine, the separatists and Russia.
Anwar, who is also Permatang Pauh MP, said possibly the government had acted well quietly, and seized the opportunity to go into the crisis area.
"Hence, I take a middle view in Najib's handling of the matter. Malaysia must be stern to ensure the safety of airspace and the affected crash sites for the safety of the Malaysian officials going there.
"I urge the government to be sterner in matters pertaining to justice," Anwar said, adding that he also hoped the government would not forget the plight of the people of Gaza.
Ambiga, in a Twitter post, also commended Najib's handling of the matter, calling it a "good job."
Najib had in his press conference last night, said Malaysia had negotiated for the handover of the black boxes to Malaysian officials.
The two black boxes were returned early this morning, by the Ukrainian separatists following discussions with their leader, Alexander Borodai.
Meanwhile, Penang Chief Minister Lim Guan Eng agrees with Najib that in conflict regions with divided authority, engaging in diplomatic channels quietly is the best means to achieving the desired results.
"DAP is willing to stand together with the federal government to support their efforts to bring back the bodies to the families so that a decent and dignified burial can be conducted.
"The DAP is also willing to stand with the federal government to vigorously pursue investigations to ensure that justice can be done against the perpetrators for the innocent lives lost," he added in a statement today.