UPDATE 1-Libya's two largest oil export terminals closed again
* Es Sider and Ras Lanuf ports closed again
* Armed guards who were previously on strike re-impose closure
* No crude oil tankers able to load
* About 15 crude and oil product tankers waiting
LONDON, Aug 12 (Reuters) - Striking security guards again halted loadings at Libya's two largest crude oil export terminals, Es Sider and Ras Lanuf, after operations had resumed briefly following a two-week outage, trading and shipping sources said on Monday.
The port outages, coupled with strikes and protests at other oil installations, have caused the worst disruption to the North African OPEC member's oil industry since the civil war in 2011.
The stoppage had been lifted on Sunday at the Es Sider terminal, which is operated by the Waha Oil Company, a joint venture between Marathon, Hess and ConocoPhillips with Libya's state National Oil Corporation (NOC).
"The security guards have stopped the exports (from Es Sider)," Mohammed El-Hattab, chairman of the federation of oil workers and an employee at Waha Oil Company, said.
"We are having discussions now and hope to restart today or tomorrow," he added.
Loadings at Ras Lanuf terminal have also stopped again after a brief resumption, the sources said. The port is operated by Harouge Oil Operations, a joint venture between Canada's Suncor and Libya's state National Oil Corporation (NOC).
No tankers have loaded although two vessels berthed at Es Sider when the port was opened, sources said. At least one tanker has been waiting outside Ras Lanuf since the end of July when the strikes began.
The two ports have a combined export capacity of around 600,000 barrels per day (bpd).
In total, around 15 crude and oil product tankers were waiting outside the two ports, according to Windward, a maritime analytics services company.