Defeating Barisan Nasional in the next general election would not necessarily require all opposition parties to be in the same coalition, Pakatan Harapan leaders said.

Sinar Harian quoted DAP's national assistant publicity secretary Zairil Khir Johari as saying that what is more important would be to pursue a cooperation between parties, whether formal or informal.

"The ideal (outcome) would be for the opposition to put up a straight fight (against BN). We have to be clear on what the opposition's goal is.

"If we want to realise the people's desire to change the (federal) government and bring down Prime Minister Najib Abdul Razak, then a cooperation would be needed. That is mandatory," he said.

The Bukit Bendera MP also said the opposition must adopt a "comparative advantage" approach in determining which party would contest in which seat.

"This means that the choice of party (to contest) must be based on the winnability principle and who has the most influence in the area," he said.

PKR vice-president Tian Chua, meanwhile, reportedly concurred with Zairil and said all opposition parties must reach an agreement to work together, despite not being in an official coalition.

"If we can unite in one coalition, it would be better. If not, at the very least we must get an agreement to work together towards putting up a straight fight," he said.

The Batu MP said this was because the straight fight concept practised by the opposition in past elections had resulted in major victories.

"I am confident the opposition can reunite in GE14 to achieve the aim of putting up a straight fight," he said, adding that PKR is willing to play a role in paving the way for cooperation among opposition parties.

Sinar Harian in a separate report also quoted Parti Amanah Negara deputy president Salahuddin Ayub as urging all opposition parties to start negotiations on a cooperation based on the common goal to bring down BN.

"Before deciding on who would contest (in which seat), all opposition parties must urgently agree to sit together and have a discussion.

"Only after that we can discuss on seat distributions and other matters," he said.

Amid speculations of GE14 being called before 2018, former premier Dr Mahathir Mohamad's Parti Pribumi Bersatu Malaysia (Bersatu) is the newest party set up to oppose BN.

His recent reconciliation with jailed PKR de facto leader Anwar Ibrahim was widely seen as being the new uniting force for the opposition.

Aside from Pakatan Harapan comprising DAP, PKR and Amanah, the federal opposition is also represented by Parti Sosialis Malaysia and PAS which has since formed a third bloc with Parti Ikatan Bangsa Malaysia.