A fierce border battle between Thailand and Cambodia raged for a second day and spread to new fronts on Tuesday, as both countries accused each other of shelling civilian areas and Bangkok vowed to push on with its planned military operations.

With the neighbours trading blame for starting Monday's renewed clashes, it was unclear how or if a fragile ceasefire brokered by U.S. President Donald Trump in July could be salvaged.

A top adviser to Cambodia's Prime Minister Hun Manet late on Tuesday told Reuters his country was "ready to talk at any time", but Thailand's foreign minister in an interview said he saw no potential for negotiations, adding the situation was not conducive to third-party mediation.

Thai tanks fired shells into a border casino complex being used by Cambodia's army as a weapons storage area, Thailand's army said, as fighter jets carried out air strikes for a second day on what the air force said were strategic military targets.

Thailand has made clear its intent is to dent its neighbour's ability to launch attacks, with a top general on Monday saying the army's objective was to "cripple Cambodia’s military capability for a long time to come"

Cambodia's Defence Ministry said its troops had no choice but to take defensive action on Tuesday, accusing Thailand of "indiscriminately and brutally targeting civilian residential areas" with artillery shells, allegations Bangkok rejected.

U.S. Secretary of State Marco Rubio in a statement called for an immediate halt to hostilities and for a resumption of de-escalatory measures agreed at an October summit in the presence of Trump.
'WE CAN'T STOP NOW,' SAYS THAI PM
The fighting is the most intense since a five-day exchange of rockets and heavy artillery in July that marked their heaviest clashes in recent history, when at least 48 people were killed and 300,000 displaced before Trump intervened to broker the ceasefire.

Both countries have said they have evacuated hundreds of thousands of people from border areas. Cambodia's Defence Ministry said nine civilians had been killed since Monday and 20 seriously injured, while Thai officials said four soldiers had been killed and 29 people injured.