They are among thousands of people driven from their homes since the Iran-backed rebels launched a broad offensive in areas near the Red Sea last week, their biggest in years.Choking back tears as she shelters in a rudimentary hut of wood and straw, the mother describes her anguish for her four adult children who were unable to escape, trapped by the fighting."I fled on my own, terrified, on one of my sons' motorcycles. We have nothing left," said the woman in her fifties from the Muthalath al-Udain area of Hodeida province."We were forced to leave because of the Houthis," she told AFP, adding: "My children are still there -- they couldn't get out. I weep for them every day, waiting for them to escape."Yemen's long-running conflict has flared into life after a four-year truce unravelled in July, as regional tensions rocketed during the Middle East war.More than 500 people have died in clashes between the Houthis and Saudi-backed government forces since last week, according to sources on both sides. The Houthis are trying to seize territory along the Red Sea, where they have been attacking Saudi tankers. The route has become key for Saudi oil since Iran blockaded the Strait of Hormuz, a major route for Gulf shipments.Meanwhile a wave of Houthi attacks on Tuesday set Saudi oil sites ablaze and wounded dozens of people. On Wednesday, the rebels reported more than 40 Saudi reprisal strikes.'We're exhausted'The renewed fighting in southwest Yemen has forced nearly 20,000 people to flee their homes, according to the International Organization for Migration.