Create and Update node using same form via ajax with form_state values

Hi
I'm trying to create and update node using same form.
for ex: example.org/node/add/example
once i create a fresh node using node creation form via ajax i need to update same node on same form. But at the moment its always creating new node instead of update. When i debug form_state['node'] its has created node id but when i use call_back function for submit its creating new node. I used node_form_submit($form, $form_state); on callback function.
How do i update node after create it using ajax.

Thanks