WASHINGTON - US first lady Michelle Obama will travel to Africa on Sunday with daughters Sasha and Malia and her mother as part of an effort to promote girls' education, her office said.The upcoming, six-day trip will include visits to Morocco and Liberia. She will also visit Spain. The trip will highlight the work of Let Girls Learn, a US government initiative launched by US President Barack Obama and the first lady in 2015.That project is part of "a US government effort to address the barriers that keep over 62 million girls around the world out of school, particularly adolescent girls," the first lady's chief of staff, Tina Tchen, told reporters on a conference call.Michelle Obama will be joined by actresses Meryl Streep and Freida Pinto in Morocco, where they will talk to adolescent girls on the challenges they face in getting an education, her office said.In Liberia, she will visit a US Peace Corps training facility and a school along with Liberian President Ellen Johansson Sirleaf, Africa's first female elected head of state and a Nobel Peace Prize winner.Michelle Obama's interest in education for young girls was heightened after militant Islamist group Boko Haram seized 276 girls from their school in Chibok, northeast Nigeria, in April 2014. She highlighted their plight through a Twitter hashtag, #BringBackOurGirls."This is a unique trip in the sense that the first lady is going to three different regions that are important to the United States: Sub-Saharan Africa, North Africa and Europe," Ben Rhodes, assistant to the President, told reporters on the same call.