UPDATE 1-Libya's oilfields producing Es Sider, Amna and Sirtica shut

* Output of main grade Es Sider halted completely

* Operations at major terminals still down due to strike

* Zueitina port and El Feel oilfield still shut from other protests

LONDON, Aug 7 (Reuters) - Output of Libya’s main crude oil grade, Es Sider, has been completely shut down since Tuesday, along with the fields producing Amna and Sirtica, following strikes at the Es Sider and Ras Lanuf terminals, Libyan and trading sources said.

The outage is one of the worst disruptions the OPEC member has seen in the last year, with exports down to about 425,000 barrels per day (bpd) from previous levels of more than 1 million bpd.

“The whole of Es Sider fields have stopped producing,” a senior Libyan industry source said on Wednesday, adding Sirtica and Amna output was also completely down. Es Sider is Libya’s main export grade.

Another source said the fields were shut down because they had reached maximum storage capacity as exports had been halted for more than a week.

The country’s main terminals of Es Sider and Ras Lanuf have been down since end July due to protests by armed guards, who normally secure the installations, over pay and other issues.

Trading and shipping sources said that port operations were still stopped on Wednesday. The smaller oil terminal of Zueitina was also down due to another protest, which began mid-July.

Ras Lanuf and Es Sider together are able to handle about 600,000 bpd. Zueitina had been exporting up to 70,000 bpd.

Libya’s oil minister said on Monday the government was working to end the protests by meeting with the families of the protesters and appointing a new head of the oil security force.

The light sweet Es Sider grade is produced from multiple fields by the Waha Oil Company, a joint venture between Hess , Marathon and ConocoPhillips and Libya’s National Oil Corporation (NOC). Production capacity is around 350,000 bpd.

The Harouge Oil Company is a joint venture between Canada’s Suncor and NOC, which operates the Ras Lanuf terminal and the fields producing Amna and Sirtica.

The El-Feel oilfield, with production capacity of 130,000 bpd, has been shut since end-May. The field is operated by Mellitah - a joint venture between Libya’s state energy firm and Italy’s Eni.