Story highlights A large explosion rocked Damascus,Syria-focused human rights group says

State-run news agency cites a "terrorist" attack on a power plant in southern Damascus

Activists post video of fire

In London, the main opposition umbrella group lists conditions for a planned conference

Syria was plunged Wednesday into a nationwide blackout, the state-run Syrian Arab News Agency reported.

A "terrorist attack on the gas feeder line for a power plant" in southern Damascus led to "power outages in all provinces" and efforts were under way to restore it, Electricity Minister Imad Khamis told SANA.

Syrian activists were posting video to social media accounts showing what they described as a gas line fire near the Damascus airport. The video showed unidentified buildings in the dark, with a fire burning on higher ground behind the structures.

And the Syrian Observatory for Human Rights reported that a large explosion rocked Damascus late Wednesday. The blast targeted a government checkpoint and injured soldiers there, the London-based activist group said.

In London on Wednesday, at a meeting of the "Friends of Syria," the head of Syria's main opposition umbrella group laid out a list of conditions for participation in a conference to be held by the end of the year in Geneva with the goal of ending the bloodshed that has wracked the country since March 2011.

Ahmad al-Jabra, leader of the Syrian National Coalition, said they include:

-- releasing prisoners;

-- lifting the siege from affected areas and allowing the entry of aid;

-- stopping the use in civilian areas of ballistic missiles, cluster bombs and fighters jets;

-- the departure from Syria of Hezbollah and Iranian Revolutionary Guard forces;

-- the renewal without conditions of ex-pats' Syrian passports;

-- a commitment from President Bashar al-Assad to implement the provisions reached in the first such conference, dubbed Geneva 1;

-- a declaration by al-Assad to accept a transition of power to an interim government body with executive powers, written in the constitution;

-- an agreement by all sides that the transitional government is the sole source of legitimate law in the country;

-- an agreement that the U.N. Security Council will guarantee any agreement under Chapter VII of its charter, which would allow military action;

-- a timetable for the transition;

-- stipulation that those responsible for war crimes against humanity be removed from power and held accountable.

British Foreign Minister William Hague told reporters Wednesday that al-Assad should play no political role in Syria.

The opposition Local Coordination Committees of Syria said at least 33 people were killed Wednesday across Syria.

State-run SANA said at least 10 people were killed in "terrorist" attacks in Damascus and Aleppo.