Cambodia's influential former leader Hun Sen said Tuesday his country had retaliated in reignited border clashes with neighbour Thailand, after Phnom Penh denied firing back for two days.

"After being patient for more than 24 hours in order to respect the ceasefire and for time to evacuate people to safety, yesterday evening we retaliated with more (responses) last night and this morning," Senate president and former prime minister Hun Sen said in a Facebook post.

"Our forces must fight at all points that the enemy has attacked," he said, while telling troops to "implement the strategy to destroy the enemy forces".

"Now we fight in order to defend ourselves again," he added.

Five days of combat this summer between the two Southeast Asian nations killed 43 people and displaced around 300,000 on both sides of the border before a truce took effect.

Renewed combat this week has killed six Cambodian civilians and a Thai soldier, and wounded more than 20 others.

The two countries have blamed each other for the fresh fighting, which saw Thailand launch air strikes and use tanks against its neighbour on Monday.

Cambodia's defence ministry spokeswoman Maly Socheata had maintained on Monday that Cambodian forces had not retaliated against Thai attacks.

© Agence France-Presse