Police in Cambodia blocked an opposition protest march on Monday, but avoided violence by allowing a convoy of opposition lawmakers to drive through to present a petition complaining of government intimidation to the king.

The compromise, which kept grassroots opposition supporters from marching to the royal palace, came after the two sides traded threats in reaction to intensifying government pressure on political opponents.

Critics say Prime Minister Hun Sen is stepping up his attacks on the opposition Cambodia National Rescue Party to cripple it ahead of the 2018 general election. The opposition mounted a surprisingly strong challenge to Hun Sen's ruling Cambodian People's Party in the 2013 general election, which it says it would have won if the government had not committed alleged electoral fraud..

The government recently accused deputy opposition leader Kem Sokha of carrying on an illicit love affair. The tangled case, which began with recordings of intimate phone calls posted anonymously on the internet, has resulted in a series of charges and counter-charges that could lead to Kem Sokha losing his seat in Parliament, or even being imprisoned.

Earlier Monday, at a National Assembly session boycotted by the opposition, government lawmakers voted to endorse court orders allowing the arrest of Kem Sokha.

The government pressure, which began last year, is widely seen as aimed at weakening the opposition by depriving it of strong, charismatic leadership. Opposition leader Sam Rainsy is in exile to avoid imprisonment over a separate legal matter also seen as politically motivated.

Police set up a roadblock Monday about 500 meters (yards) from the opposition party headquarters, from which more than 1,000 followers were planning to march to the royal palace to present a petition to King Norodom Sihamoni to support their demand that the government stop arresting and intimidating opposition members.

After a standoff of about an hour, during which tensions were high but no clashes broke out, 23 vehicles carrying opposition officials were allowed to pass through. Police Col. Prum Channa said the opposition supporters lacked legal permission to march and could harm public order.