MEXICO CITY, Oct 22 (Reuters) - Operations at Mexican national oil company Pemex"s Tula refinery resumed two days ago after a three-week closure due to rail and road blockades by protesting teachers, a company source with knowledge of the matter told Reuters on Friday. The protest in particular hit the refinery"s ability to transport a growing stockpile of fuel oil, burned to generate electricity by plants owned and operated by state-run power company CFE. The Tula refinery located just north of Mexico City in Hidalgo state is the country"s second biggest with a daily crude oil processing capacity of 315,000 barrels. But for an extended period it has operated far below its capacity, processing an average of 153,400 barrels per day (bpd) this year through August, according to company data. "Tula began operating again on Wednesday," the company source said, speaking on condition of anonymity. Pemex"s press office did not immediately respond to a request for comment. President Andres Manuel Lopez Obrador told reporters at his regular morning news conference on Friday that the Tula facility was producing after he was asked if it remained closed. "We do not have reports of problems," he said, noting that the protesters" blockade might have affected the movement of fuel oil from the plant. "This prevents fuel oil produced in Tula from getting to the port of Lazaro Cardenas via train," said Lopez Obrador, referring to the major shipping hub on Mexico"s Pacific coast. Fuel oil is a by-product of the refining process used by several of the CFE"s biggest power plants, and Lopez Obrador said tanker trucks were being used to transport it. The president added that the government has paid teachers what they were owed in back pay, and that this action should resolve the protests. Reporting by Ana Isabel Martinez; Editing by David Alire Garcia and Bill Berkrot