No Trump! the rally of hundreds shouted, growing louder as it neared the United States embassy in the centre of South Korea's capital Seoul.

A line of police buses stopped them reaching the gates, but a stage and loudspeaker ensured their voices would soar above Gwanghwamun square and within earshot of US President Donald Trump's representatives.

This was a small rally by the standards of South Korea's vibrant protest culture. And it was not the only one under way. A few hundred metres to the north, at the gates of Gyeongbokgung palace, marchers held aloft more banners as they chanted a very different message.

No China, along with a smattering of CCP [Chinese Communist Party] out!. Again, the numbers - several hundred people - were not huge for South Korea.

Nevertheless, this footfall through central Seoul on a sunny Saturday is an indication of the diplomatic dance South Korea's President Lee Jae Myung will have to perform this week as he hosts the leaders of both the US and China.

Seoul is - and has long been - a key US ally. A friendship forged in blood, as its leaders often say, during the Korean War from 1950 to 1953, when American troops helped repel the North Korean invasion. The South still needs Washington's protection, but it also needs China, its biggest trading partner and a vital market for exports.

It's a particularly fraught moment - South Korea finds itself caught between a rock and a hard place, says Darcie Draudt-Vejares, from the Carnegie Endowment for International Peace.

Year after year it epitomizes the choice of many countries worldwide that are deeply economically integrated with China, but also with the US. Right now, Lee Jae-myung is trying to maneuver between these superpowers.

Lee's work is particularly demanding this week as he orchestrates talks between Trump and Xi Jinping that could lead to a breakthrough in their ongoing trade disputes.

At 61, Lee is a seasoned politician, but he has inherited a nation divided by recent political turbulence, notably stemming from the impeachment of his predecessor, Yoon Suk Yeol.

Under Lee, South Korea sought to strengthen ties with the US, pledging significant investments. However, tensions have risen following a large immigration raid affecting Hyundai workers in the US, complicating these relationships.

Meanwhile, anti-China sentiments simmer as protests against Chinese influence grow, with citizens expressing deep desire for a balance in international relations while confronting perceived aggressions.

As President Lee prepares to meet both leaders, South Korea's ability to maintain its economic interests and national security remains precarious, with much at stake during this high-profile diplomatic engagement.