LONDON (Reuters) - Up to 100 additional British troops will join U.N. peacekeeping work in South Sudan, the defense minister said on Thursday, taking the total to around 400.

Defence Secretary Michael Fallon said the deployment, which supplements the 300 British personnel already in the region, could help reduce the number of migrants fleeing poverty and war in Africa and the Middle East from traveling to western Europe.

"This large scale deployment underlines how we are stepping up our global commitments," Fallon told a conference of defense ministers.

"Backed by a rising defense budget, it's part of our effort to tackle the instability that leads to mass migration and terrorism. It will help keep Britain safe while improving lives abroad."

Last month, the United Nations Security Council authorized the deployment of 4,000-strong protection force in South Sudan's capital Juba after several days of fighting involving tanks and helicopters between troops loyal to President Salva Kiir and those backing former Vice President Riek Machar.

(Reporting by Elizabeth Piper; editing by Michael Holden)