Ugandan rebels on Thursday fired on a UN helicopter in an attack in the volatile east of Democratic Republic of Congo, though there were no victims, UN sources said."One of our helicopters was fired on in Semuliki valley by rebels - we reacted in legitimate defence," French General Bernard Commins, deputy head of the MONUSCO UN peacekeeping force told AFP."The aircraft was able to land without problems but it had been hit," added Commins.The attack came in the eastern region of Beni, where last week eight UN peacekeepers died in a clash with Allied Democratic Forces (ADF), a Ugandan jihadist group blamed for bloody attacks on civilians.The region is rich in coltan, a mineral which when refined is a key element in electronic devices.The Islamist-rooted ADF, active in eastern Democratic Republic of Congo since 1995, killed 15 peacekeepers in an attack in November last year at Semuliki near the Ugandan border.In the worst skirmish since then, last week's attack saw eight killed and 12 injured while 12 DRC soldiers backing the UN force also died.The group, forced out of Uganda as they oppose President Yoweri Museveni, live in the jungle and operate in the border area in the DRC's North Kivu province. The ADF is led by Jamil Mukulu, a Christian turned Muslim.The group has yet to launch large-scale attacks inside Uganda but is blamed for the deaths of hundreds of civilians since late 2014.MONUSCO has around 17 000 members, making it one of the UN's biggest peacekeeping operations. Created in 1999 during the Second Congo War, it has an annual budget of $1.153 billion.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.