Cambodia's powerful Senate President Hun Sen on Tuesday vowed a fierce fight against Thailand as a second day of widespread renewed combat between the Southeast Asian neighbors drove tens of thousands of people to flee border areas.

At nine months pregnant, 27-year-old Suang Sreang fears she will have to give birth in a rudimentary displacement camp after fleeing fighting between Cambodian and Thai troops along their disputed border.

Cambodia says Thailand has launched more airstrikes as heavy fighting flares along their border. Both countries accuse each other of violating sovereignty.

Armed clashes between Thailand and Cambodia entered a second day on Tuesday, both sides said, in defiance of calls from the United States to stop fighting and adhere to a months-old Trump-brokered peace deal that now looks on the brink of complete collapse.