US President Donald Trump has underscored his controversial travel ban on citizens from six Muslim-majority countries in view of today's terror attacks in central London.<br/> <br/>Trump said in a tweet, "we need to be smart, vigilant and tough. We need the courts to give us back our rights. We need the Travel Ban as an extra level of safety.''<br/> <br/>Trump in his executive order had banned visa issuance to citizens of six majority-Muslim countries – Iran, Libya, Somalia, Sudan, Syria and Yemen.