(Fixes spelling error in the headline) By Anton Zverev DONETSK, Ukraine (Reuters) -Staff of the Organisation for Security and Cooperation in Europe (OSCE), which has been monitoring the situation in eastern Ukraine, began to pull out of the rebel-held city of Donetsk on Sunday as fears of a possible Russian invasion grew. A Reuters journalist saw several armoured cars being loaded suitcases and leaving the mission’s headquarters. The OSCE said in a statement that “certain participating states” had told their citizens at the mission to leave within the next days. It did not name the countries b…