US carrier Southwest Airlines grounded its flights on Tuesday due to a problem with its reservation system, the Federal Aviation Administration (FAA) said. "The FAA issued a temporary nationwide ground stop at the request of Southwest Airlines while the company resolved a reservation computer issue," the regulator said on Twitter. The problem is the second in a 24-hour stretch for the domestic-focused carrier, which delayed more than 1,400 flights across the United States on Monday due to problem with a third-party weather data provider. At 1950 GMT, Southwest said on Twitter it was ramping back up after the outage. "Southwest is in the process of resuming normal operations after a brief pause in our flight activity resulting from intermittent performance issues with our network connectivity Tuesday afternoon," a company spokesman said in an email to AFP. "Our teams are working quickly to minimize flight disruptions and customer impact." jmb/cs