DAKAR (Reuters) - A long-awaited multi-national military force in Africa s Sahel region has begun operations to counter escalating Islamist insurgencies, participants in the joint effort said on Thursday.     The G5 Sahel force, backed by France and the United States, launched its campaign on Oct. 28 amid growing unrest in the desert reaches of the Sahel, where jihadists such as al Qaeda and Islamic State-affiliated groups roam undetected, often across long, porous borders.  Last month, Islamist militants killed four U.S. soldiers and at least four Nigeriens in an ambush that highlighted the risks of operating in the remote region. G5 Sahel is made up of troops from Mali, Niger, Chad, Burkina Faso and Mauritania that will police the region in collaboration with 4,000 French troops deployed there since intervening in 2013 to beat back an insurgency in northern Mali.  The first mission, called  HAW BI , comprises several hundred soldiers from Mali, Niger and Burkina Faso, whose shared borderlands have been the epicenter of a surge in militant attacks, G5 Sahel said in a statement.   The operation...aims to achieve an area of control in this region of three borders to fight against armed groups and trafficking, in order to allow the return of a level of security favorable to the tranquility of the populations,  the statement said. The force will eventually swell to 5,000 men from 7 battalions and will also engage in humanitarian and development work, it said.  G5 Sahel, whose command base is in Sevare in central Mali, will also coordinate with MINUSMA, Mali s U.N. peacekeeping mission. MINUSMA has faced frequent attacks in the north where Islamists have regained ground since 2013.  The new force faces a number of challenges, not least in funding. The United States this week promised up to $60 million in support, but that fell short of hopes by France and others that Washington would back direct funding from the United Nations. 
G5 Sahel launches military operation in African scrublands