SEOUL (AFP) - South Korean President Park Geun Hye fired her spokesman over an unspecified "unsavoury" act midway through a summit trip to the United States (US) this week, Yonhap news agency reported on Friday.

Senior presidential press secretary Lee Nam Ki announced Yoon Chang Jung's dismissal, saying he was "personally involved in an unsavoury incident", described as "an inappropriate act for a high-level official" that "hurt national dignity."

Mr Lee did not elaborate but said South Korea's embassy in Washington was looking into the incident and the findings would be made public.

Mr Yoon had returned to Seoul from Washington on Wednesday without accompanying Park on her visit to Los Angeles, the final stop of her visit to the US, sparking speculation on why he cut his trip short, Yonhap said.

Earlier this week, Ms Park held a summit with President Barack Obama, with the two leaders united in a vow to offer no concessions when dealing with North Korea.

Ms Park also addressed a joint session of the US Congress, stressing that Pyongyang had to give up its nuclear weapons while also proposing small peace steps after months of sky-high tensions.