(Updates with death of protester) GAZA, Sept 1 (Reuters) - A teenage Palestinian protester was killed as tens of thousands of Gazans demonstrated in the southern part of the strip on Saturday against the closure of a border crossing with Egypt. The demonstration lasted several hours and broke up after dark, local security officials said. Hospital staff named the dead as 17-year-old Mohammed Qdaih who was accidentally hit by a bullet fired by Hamas Executive Force officers trying to keep the crowd under control. The demonstration took place at the Rafah border crossing which connects the Gaza Strip with Egypt. It is the only direct link between Gaza and the outside world that does not go through Israel. The crossing has been closed since Hamas seized control of the Gaza Strip from forces loyal to Palestinian President Mahmoud Abbas in June. Rafah was technically controlled by Abbas's forces and monitored by European Union observers before Hamas's takeover, although Israel frequently shut it down citing security grounds. The other side of the crossing is controlled by Egypt. Last month, several thousand Palestinians who were stranded in Egypt for weeks, were allowed to return to the Gaza Strip through Israeli crossing points which forced the returnees to travel via Israel. Hamas rejected the deal between Israel, Abbas and Egypt to open those crossings instead of Rafah, saying it set a dangerous precedent by reducing pressure on the Jewish state to reopen Rafah any time soon.