US Secretary of State Rex Tillerson says the US is considering sanctioning oil imports from Venezuela. He was speaking during a visit to Argentina. Tillerson said US would also stop exporting refined products to Venezuela to urge President Nicolas Maduro to "return to the constitution". Oil exports have been an important source of revenue for crisis-hit Venezuela. Crude oil sales to the US in 2017 were the lowest since 1991. Previous US sanctions focused on members of the Maduro government and a ban on buying new Venezuelan debt. Argentine Foreign Minister Jorge Faurie said Argentina is also considering oil sale restrictions. But other Latin American countries have expressed unwillingness to take steps to worsen the crisis in Venezuela.