PHNOM PENH, Cambodia (AP) — Cambodia's opposition party on Wednesday threatened a nationwide general strike to protest what it says was a rigged election and the illegitimate return to power of Prime Minister Hun Sen.

Opposition leader Sam Rainsy said he is considering calling a one-day strike for factory workers, civil servants and shopkeepers unless the ruling party agrees to an independent probe of electoral fraud and a program of immediate reforms.

He made the comments a day after ruling party lawmakers extended Hun Sen's rule for another five years, despite a boycott of parliament by the opposition.

Hun Sen, speaking to his newly formed Cabinet for the first time, rejected allegations his government was not legitimate.

"Some people said that our government has not been recognized, but for us ... the stamp of legitimacy comes from" King Norodom Sihamoni, Hun Sen said.

"You can call this royal government whatever you want, but it is a legitimate government," he said.

Official results of the July 28 polls gave the ruling party 68 seats in parliament compared to 55 for the opposition. The opposition says it was cheated out of victory and has staged several mass demonstrations against the election results.

Sam Rainsy said his Cambodia National Rescue Party would announce its protest strategy in the next few days but was debating calling for a general strike.

"The whole country for one day will hold a strike. All factories, all civil servants, all shopkeepers will stop working that day — this is one possible idea," he said.

The opposition leader also called on the international community and foreign companies to stop engaging with the government.

"We will conduct a worldwide campaign to delegitimize this government, which is the result of a constitutional coup and which does not represent the Cambodian people," he said.

Hun Sen's ruling party performed unexpectedly weakly in the election, emerging with its poorest results in more than a decade to see its majority wither in the 123-seat National Assembly. The opposition, running on a newly unified slate, meanwhile boosted its number of elected lawmakers to 55 from 29.

Sam Rainsy said the opposition's boycott of parliament, which convened Monday, will continue until the government meets its demands.

"We will not cooperate in any manner with the present National Assembly and with the present government unless there are guarantees" of a probe into election results and that reforms will be made, he said.

He called for a moratorium on land grabbing and deforestation, two major complaints against Hun Sen's government in recent years.