UPDATE 1-Wheat price spike raises food insecurity-UN expert

* U.N. expert blames trader speculation for costlier food

* Floods in Pakistan, drought in Syria also strain supplies

(Adds comments on Syria hunger, Mozambique on bread prices)

By Laura MacInnis

GENEVA, Sept 7 (Reuters) - Riots over high bread prices in Mozambique and food shortages elsewhere should be a wake-up call for governments which papered over food security problems that arose two years ago, a United Nations expert warned on Tuesday.

Olivier De Schutter, the U.N. special rapporteur on the right to food, said during a mission to Syria that donors had not been delivering on their aid promises and that public anger in countries like Mozambique was predictable.

"Most poor countries are still highly vulnerable," De Schutter said in a statement. "Their food security is excessively dependent on food imports whose prices are increasingly high and volatile."

In Mozambique, 13 people were killed and nearly 150 arrested last week after riots sparked by a 30 percent rise in the price of bread -- a result of soaring global wheat prices.

In response, the government announced on Tuesday that it would reverse the bread price increases, using subsidies to cover the costs.