The weekly average crude oil price of the Organization of Petroleum Exporting Countries (OPEC) dropped by 3.80 U.S. dollars to 68.57 dollars per barrel last week, the cartel's secretariat said Monday.

The ongoing mortgage crisis in the United States is being cited as one of the main factors in the price plunge.

Meanwhile, OPEC's daily average oil prices dipped to 67.52 dollars per barrel last Friday, going lower than 68 dollars per barrel for the first time since the historical high of 73.67 dollars was registered on July 20.

Analysts believe the drop in oil prices could be attributed to investor speculation prompted by the mortgage crisis, which in turn could affect global economic growth and crude oil demand -- even after effective measures by the Federal Reserve.

But the analysts stressed that international oil prices could rebound and hit a new record after amid the current unstable phase.

The International Energy Agency predicted that global crude oil demand would remain strong, and called on OPEC to increase output.

OPEC, however, hinted at no output increase at the next ministerial conference in September.