May 11 (Reuters) - The Rwandan-backed AFC/M23 rebel group has withdrawn from several key positions in Congo's eastern South Kivu province over ‌the weekend, the Congolese army and a rebel official said ‌on Monday, marking the first significant battlefield shift in months.

• The withdrawal followed military pressure ​from the Congolese army and diplomatic pressure from Washington, a spokesperson for Congo's army told Reuters.

• It marks the first notable frontline movement since the rebels briefly took the city of Uvira in December before withdrawing under pressure ‌from the United States. ⁠It comes two weeks after the U.S. imposed sanctions on former president Joseph Kabila over alleged links to AFC/M23, ⁠allegations he denies.

• The rebels pulled back from Kabunambo, some 35 kilometres north of Uvira, to Luvungi, roughly 30 kilometres further north towards the provincial ​capital Bukavu, ​where they were stationed before their ​advance on Uvira, the two ‌sources said.

• Congolese families who fled last year's violence to neighbouring Burundi have begun returning home, a civil society leader in Uvira told Reuters.

• Fighting has continued in eastern Congo despite mediation efforts led by the United States and other international actors.

• In a letter to U.S. Secretary of ‌State Marco Rubio dated May 7 and ​shared with media over the weekend, AFC/M23 ​political coordinator Corneille Nangaa accused ​the U.S. of lacking credibility as a mediator, after ‌signing a key minerals partnership deal ​with Kinshasa last ​year.

• The State Department did not immediately respond to a request for comment on Monday.

• Rwanda has denied accusations by the United ​Nations and Western governments ‌that it supports the insurgents.

(Reporting by Congo newsroom, Ange Kasongo in ​Kinshasa, Stanis Bujakera in Washington and Clement Bonnerot in Dakar; ​Editing by Robbie Corey-Boulet and Sanjeev Miglani)