The United States has ordered all nonessential diplomats and their family members to leave Yemen as the country spirals into civil war. At least 72 people have died there over the past three days in confrontations between tribal fighters and government forces. On Thursday, several explosions were heard in the capital, Sanaa, with the government reportedly shelling residential neighborhoods. One explosion overnight killed at least 28 people. The fighting is spreading to other parts of the country as well. Yemen’s president, Ali Abdullah Saleh, has promised three times to sign a power-transfer agreement before backing out at the last second.