Washington (dpa) - After drone strikes on the largest oil refinery in Saudi Arabia, US President Donald Trump has approved the release of national oil reserves in the event of bottlenecks. The amount he has not yet set, but it will be sufficient "to supply the markets well," Trump tweeted. US strategic oil reserves are 630 million barrels, according to the US Department of Energy. Saudi Arabia produced about 9.8 million barrels of oil per day last month, according to OPEC.