Emergency teams work at the site of a derailed electric streetcar in Lisbon, Portugal on Wednesday. (Armando Franca | AP)LISBON, Portugal — Portugal observed a national day of mourning Thursday, a day after a famous Lisbon streetcar derailed and killed 15 people in the capital’s worst accident in recent history. Portuguese President Marcelo Rebelo de Sousa offered his condolences to affected families, and Lisbon Mayor Carlos Moedas said the city was in mourning. Portugal’s government announced that a day of national mourning would be observed Thursday. “A tragic accident … caused the irreparable loss of human life, which left in mourning their families and dismayed the whole country,” it said in a statement.