The top nuclear negotiators of South Korea and the U.S. sat down for talks in Seoul on Thursday amid concerns that tensions could rise on the Korean Peninsula this month.

South Korea’s chief nuclear envoy Kim Gunn and his U.S. counterpart, Sung Kim, agreed to keep a close eye on the possibility that North Korea may engage in further provocations, concurring on a strong response with their countries’ combined defense readiness.

The two officials strongly agreed to encourage the international community to thoroughly implement UN Security Council resolution 2397 amid signs that the North is opening its borders.

Although the 2017 resolution requires UN member states to repatriate all North Korean laborers earning income abroad by the end of 2019, repatriation efforts hit a snag after the North shut its borders in response to the COVID-19 pandemic.

Signs that the country may be reopening, however, have emerged after China’s newly-appointed ambassador to the North, Wang Yajun, entered the reclusive state earlier on Monday.

Meanwhile, Seoul’s nuclear envoy is set to meet his Japanese counterpart, Takehiro Funakoshi, later in the day before a trilateral meeting of the three envoys on Friday.