UPDATE 1-U.N. takes over Chad force amid growing Darfur fears

* United Nations takes over control of European Union force

* Bashir arrest warrant heightens fears of violence

* Darfur aid groups' expulsion may send refugees over border

(Adds troop numbers, quote from UN peacekeeping head)

By Moumine Ngarmbassa

ABECHE, Chad, March 15 (Reuters) - The United Nations took over command of an EU protection force in eastern Chad on Sunday, and there were growing fears of more rebel violence and the possible arrival of tens of thousands more refugees from Sudan's Darfur.

The European Union formally handed over command to the U.N. mission in Chad and Central African Republic (MINURCAT) at a ceremony in Chad's eastern city of Abeche on Sunday morning after Eufor's year-long mandate expired at midnight.

The handover, which sees around 5,000 U.N.-commanded troops replace an EU force of close to 3,500, takes place at a time of heightened tension after the International Criminal Court issued an arrest warrant this month against Sudanese President Omar Hassan al-Bashir for alleged war crimes and crimes against humanity in Darfur.