JSONModel not loading from URL

I am trying to fetch JSON data from RESTFUL service when I use below code, loadModel() is not loading the data.

var oModel = new sap.ui.model.json.JSONModel();
//oModel.setData();
oModel.loadData("URL to my RESTFUL SERVICE");

Should I use .ajax call to load the data from RESTFUL Service similar to jQuery? in SAPUI5 too?