The offer, made on Thursday after a public reconciliation between Hun Sen and chief opposition leader Sam Rainsy, was welcomed promptly.
It might be accepted, said Meng Rita of Sam Rainsy's eponymous party.
"But our position will still be the same - to fight corruption and work for the interest of our people," Meng Rita said.
Hun Sen told a national conference on poverty reduction that the country, which has a long history of fractious politics, needed to work together as it recovered from the bloody Khmer Rouge years.
"Our people went through so much suffering, I need to gather all kinds of resources to work for the interests of the people regardless of whether they are the opposition," he said.
"I will mobilise more parties to work for the next government, including the opposition party if they want to."
Sam Rainsy has returned home
after a year in exile
The offer came days after Sam Rainsy returned from a year of self-imposed exile in France during which he was sentenced to 18 months in jail on criminal defamation charges that Hun Sen had brought against him.
That, along with several similar cases, prompted criticism of Hun Sen from abroad, particularly from key aid donors to a country where an estimated 28% of the 13 million people live below the poverty line.
But Cambodia's main political leaders patched up their differences this month and Sam Rainsy returned home, declaring a new era.
Hun Sen's Cambodian People's Party (CPP), which won 73 seats in the 123-seat parliament in the 2003 polls, is expected to win the next election.