US power is able to extend its sanctions beyond the US
US applies its sanctions beyond its own territory using it global economic and financial clout. Juan Guaido declared himself interim president of Venezuela some time ago. The US, the UK, and many other US allies recognized Guaido as the interim president and rejected Maduro. As one among many negative results, President Maduro is barred by a UK court from accessing $1.45 billion of its own gold. The court does not recognize Maduro as the president of Venezuela.
US attempts to stop Iran and Venezuela trade
Just recently US threatened to stop five fuel tankers which delivered much-needed fuel to Venezuela and parts to help repair its own refinery system. However, the five tankers made it to Venezuela without incident but were escorted by Venezuelan military vessels once they reached Venezuelan waters. Iran said it was ready to ship more fuel. Iranian foreign ministry spokesperson Abbas Mousavi told a news conference: "Iran practices its free trade rights with Venezuela, and we are ready to send more ships if Caracas demands more supplies from Iran."
Many countries fearing that they their trade with the US will be hurt if they do not follow US sanctions do so but countries such as Venezuela and Iran which are already both under severe sanctions by the US see nothing but gain by increasing trade relations. Iran can well sympathize with Venezuela as it has been at odds with the US for about a generation now.
US sanctions ship captains
The US sees the Iran and Venezuela trade as showing that its sanctions are not in effect legal so it wants to do something to try and punish if not directly stop such trade. The best it could do so far is to sanction the captains of the five Iranian ships that delivered fuel to Venezuela. US Defense Secretary Mike Pompeo spoke of the sanctions as if the US had the moral high ground: "The rogue regimes in Caracas and Tehran are unified by their penchant for repressing their people, corruption, self-enrichment, and gross mismanagement of their peoples' wealth."
Venezuela and Iran respond
Spokesperson for the Iranian mission to the UN Alireza Miryousefi said to Newsweek: "Iran considers any moves to disrupt its legitimate trade with other countries to be unlawful and illegal under international law. Iran is not threatened by U.S. bullying piracy and its unlawful pressure and will take necessary measures, in accordance with international law, to protect its interests."
Venezuelan Vice-Minister Carlos Ron also slammed US interference, claiming that the US had no right to intervene in trade relations two sovereign states. He claimed the US was violating free trade and WTO dispositions.