AlHijjah 7, 1435, Oct 1, 2014, SPA -- The first case of Ebola diagnosed in the United States has been confirmed in a man who recently traveled from Liberia to Dallas, worrying the north Texas West African community, whose leaders urged caution to prevent spreading the deadly virus. The unidentified man was critically ill and has been in isolation at a Texas hospital since Sunday, federal health officials said Tuesday. Authorities have started locating family, friends, and anyone else who may have come in close contact with the patient and could be at risk. Officials said there are no other suspected cases in Texas. Centers for Disease Control and Prevention (CDC) Director Tom Frieden said the man departed Liberia on September 19, arrived in Dallas the next day to visit relatives, and began feeling sick four or five days later. He said it was not clear how the man became infected. "I have no doubt that we'll stop this ... in the U.S. But I also have no doubt that—as long as the outbreak continues in Africa—we need to be on our guard," said Frieden, who on Tuesday updated President Barack Obama about the Dallas case and discussed isolation protocols. Stanley Gaye, the president of the Liberian Community Association of Dallas-Fort Worth, said the 10,000 Liberians in north Texas are skeptical of the CDC's assurances because Ebola has ravaged their country. "We've been telling people to try to stay away from social gatherings," Gaye said Tuesday. "We need to know who [the Dallas patient] is so that [family members] can all go get tested," he told the Associated Press. "If [CDC officials] are aware, they should let us know."