In a significant escalation of regional tensions, South Sudan's First Vice President Riek Machar has formally accused Uganda of breaching a United Nations arms embargo. In a recent letter addressed to the U.N., the African Union, and the Intergovernmental Authority on Development (IGAD), Machar contends that Uganda has deployed armored units and air force contingents within South Sudan, even conducting airstrikes that he claims have targeted civilian areas.

Machar's accusations stem from Uganda's recent military deployment, which Ugandan officials assert was made at the request of the South Sudanese government. This intervention follows a troubling deterioration in relations between Machar and South Sudan’s President Salva Kiir, particularly after a series of clashes in northeast South Sudan. In these confrontations, security forces detained several senior allies of Machar, further destabilizing the political landscape.

The peace agreement reached in 2018 aimed to resolve a devastating five-year civil war, and Uganda’s involvement is seen as a violation of this accord. Though the Sudan People's Liberation Movement-in-Opposition (SPLM-IO), led by Machar, had previously allied with the Ugandan military against Kiir's forces during the civil conflict, the SPLM-IO has since distanced itself from any ties to the White Army, an ethnic militia that the government claims supports Machar.

The U.N. has raised concerns that escalating hate speech in South Sudan could lead to renewed ethnic violence, with the potential to push the nation back into a state of war. This fear is compounded by Uganda's apprehensions that instability in South Sudan, an oil-rich country, could cause a large influx of refugees and further destabilize the region.

In his letter dated March 23, Machar urged immediate international intervention to compel Uganda to withdraw its troops, emphasizing, "The Ugandan forces are currently taking part in airstrikes against civilians." A spokesperson for Machar's office has verified the authenticity of this letter, which calls attention to the deteriorating security situation.

As of now, military spokesmen from both Uganda and South Sudan have not responded to inquiries regarding the reported violations of the arms embargo, initially imposed in July 2018. Meanwhile, conflict has intensified, with reports indicating that the South Sudanese army engaged SPLM-IO forces near the capital, Juba, on Monday night, although officials from the South Sudanese government have not yet commented on these accusations.

The deployment of Ugandan troops was retroactively approved by Uganda's parliament last week, following an announcement dated March 11. Ugandan Defense Minister Jacob Markson Oboth defended the military engagement, stating it aims to "avoid a security catastrophe" in South Sudan.

Complicating matters further, a series of controversial statements made by Uganda’s military chief, Muhoozi Kainerugaba, on social media, which included references to Machar's ethnic group, have raised alarms. These statements have historically led to heightened diplomatic tensions in the region, adding another layer of complexity to the already fraught situation.

As the international community watches closely, the unfolding events could have substantial implications for peace and stability in both South Sudan and the greater East African region.