The United States, a key supporter of South Sudan, said it was calling back its ambassador for consultations as it shows frustration with duelling leaders' failure to form a government.

US seeks to 're-evaluate relationship with South Sudan', calls back ambassador

This decade has seen massive movements of people fleeing war, poverty and persecution. Here are some key cases. Since 2011: Syria The Syrian war has killed more than 360,000 people since it began in March 2011 and it has led to a massive exodus of people, mostly to camps in neighbouring countries.

Major migration flows in the last decade

This week's clashes are the first between the army and former rebels in the capital since April

150 killed as South Sudan marks fifth independence anniversary