Iran has been racing to step up exports of petrochemicals and tap new markets to compensate for sliding oil sales, Iranian and international industry sources said, but now risks losing that crucial revenue as Washington tightens the screw on sanctions. Tehran has been selling increased volumes of petrochemical products at below market rates, in countries including Brazil, China and India, since the United States reemployed sanctions on Iranian oil exports in November, according to the six sources who include two senior Iranian government officials Iranian authorities, who do not recognize U.S. sanctions, dismissed the latest restrictions announced Friday and vowed to press on with petrochemical exports. Sarami of the exporters’ union described the American measures as “psychological warfare".