unable to parse date string of format like 2014-02-03T19:00:00

unable to parse date string of format like 2014-02-03T19:00:00

I am trying to parse date of format:
2014-02-03T19:00:00
and
2013-09-17T05:15:27.947
this is my code
String MessageRecieptDate = messageReceiptDate.Replace("T", "
").Remove(messageReceiptDate.Length-4);
DateTime dt = new DateTime();
IFormatProvider culture = new CultureInfo("en-US");
dt = DateTime.ParseExact(MessageRecieptDate, "dd MMM", culture);
but its giving some format exception everytime. seems i am missing
something basic.