Washington - The United States said on Friday it is withdrawing more than half the personnel from its embassy in Cuba in response to mysterious attacks that have sickened diplomatic staffers, in a new blow to fragile relations between the former Cold War foes.In announcing the move, Secretary of State Rex Tillerson said Washington would maintain relations with Havana - which were only fully restored in 2015, and which have deteriorated since President Donald Trump took office in January."Cuba has told us it will continue to investigate these attacks and we will continue to co-operate with them in this effort," Tillerson said in a statement."We maintain diplomatic relations with Cuba, and our work in Cuba continues to be guided by the national security and foreign policy interests of the United States." The attacks of an unknown nature have targeted at least 21 US embassy staff in Havana over the past few months, Tillerson said.Those affected have exhibited physical symptoms including ear complaints, hearing loss, dizziness, headache, fatigue, cognitive issues, and difficulty sleeping, he added."The health, safety, and well-being of our embassy community is our greatest concern. We will continue to aggressively investigate these attacks until the matter is resolved," Tillerson said.Routine visa operations will be suspended indefinitely in response to the attacks, a senior State Department official said. Cuba reacted by calling the US move hasty, and said it would affect bilateral relations.Still, Cuba wants to work with the United States to resolve this case, said the head of North American affairs at Cuba's foreign ministry, Josefina Vidal, quoted on state television."The Cuban government has no responsibility in this case and strictly respects its obligations under the Vienna Convention" governing the protection of diplomats as well as their families, she added.