Juan Guaido, the self-declared interim president, has welcomed an offer from the United States of $20 million (£15m) of food and medicines, and the supplies are being transported to the border. But Mr Maduro, who has the support of the army, will not allow it to cross the border.
On Wednesday, Venezuelan soldiers were using a fuel tanker and cargo containersto cut off access to the Tienditas bridge, which links the Colombian border town of Cucuta to Ureña in Venezuela.
Members of Venezuela’s Bolivarian national guard could also been seen at the border crossing.
The Colombian Foreign Ministry says a second crossing in the northern department of La Guajira has also been blocked.
Mike Pompeo, the US secretary of state, reacted angrily to the blockade, tweeting: “The Venezuelan people desperately need humanitarian aid. The US & other countries are trying to help, but #Venezuela’s military under Maduro’s orders is blocking aid with trucks and shipping tankers. The Maduro regime must LET THE AID REACH THE STARVING PEOPLE. #EstamosUnidosVE”
John Bolton, the US national security advisor, echoed his comments, and lashed out at Mr Maduro for seeking only to look after himself.
“Maduro and his cronies live lavishly in Europe and enrich their Cuban patrons while plundering Venezuela’s wealth,” he said. “Meanwhile, they are physically blocking the Venezuelan people, including the military rank and file, from receiving humanitarian assistance.”
He said the US would protect any senior military official who accepts Mr Guaido’s legitimacy.
“The US will consider sanctions off-ramps for any Venezuelan senior military officer that stands for democracy and recognizes the constitutional government of President Juan Guaido,” he said. “If not, the international financial circle will be closed off completely. Make the right choice!”
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Mr Maduro, increasingly isolated, has sought to sell off the country’s gold reserves to keep his regime afloat. The Bank of England, which holds $1.2 billion in Venezuelan gold, has blocked him from doing so, but Mr Maduro’s government last year sold 73 tonnes of gold to Turkey and the United Arab Emirates without the required approval of the opposition-led national assembly, an opposition politician said Wednesday.
Carlos Paparoni also said that Mr Maduro’s administration had transferred 127 million euros to bank accounts in Russia, without specifying when. Since Monday, the Venezuelan government has not been able to move money between its accounts in banks in the European Union, he added.
“We will keep working so that not one more gram of gold can be sold,” Mr Paparoni said.
The FBI raided a bank in Puerto Rico on Wednesday, on suspicion of the bank breaking sanctions placed on senior members of Mr Maduro’s government.
And the aid delivery represents the latest attempt by Mr Maduro’s political rival, 35-year-old national assembly president Mr Guaido, to weaken the Venezuelan regime by forcing members of the military to disobey Mr Maduro’s orders.
Mr Guaido on Tuesday met with former cabinet members of the late Hugo Chavez to discuss the way out of the impasse. He also met with mayors of Venezuelan cities to discuss distributing the aid.
Venezuelan opposition leaders, who have gathered in Cucuta, appealed to the Venezuelan military to allow safe passage for the aid trucks.
“You know there’s a red line, you know well there’s a limit, you know that medicines, food and medical supplies are that limit,” said Miguel Pizarro, a pro-Guaido politician.
Tents and other logistical supplies have begun to arrive in Cucuta, but the bulk of the 60 tons of aid remains in the Colombian capital, Bogota. Local officials suggested the arrival may be delayed until the border crossing is cleared, or until both sides have negotiated an agreement to let the aid pass.
The United Nations and the Red Cross expressed alarm on Wednesday about the politicisation of aid.
“Humanitarian action needs to be independent of political, military or other objectives,” said Stephane Dujarric, UN spokesman, speaking in New York.
“When we see the present stand-off it becomes even more clear that serious political negotiations between the parties are necessary to find a solution leading to lasting peace for the people of Venezuela.”
Mr Guaido wrote to UN Secretary-General Antonio Guterres last month asking for help in tackling the country’s crisis. But Venezuela’s seat at the 193-member world body is held by Mr Maduro’s government and Mr Guterres is unable to ramp up a humanitarian response in Venezuela without Maduro’s approval or UN Security Council authorisation – something which would be blocked by Russia and China.
In Geneva, the International Committee of the Red Cross (ICRC) said it was doubling its resources to cope with the crisis, where food and medicine shortages have pushed 2.3 million people to flee since 2015.
“Our focus is really to, on the one side increase our response to Venezuelans, and on the other hand to keep away from the political controversy and political divisions which are characteristic to the crisis in Venezuela,” said Peter Maurer, ICRC chief.
Walter Marquez, a former member of Venezuela´s national assembly, told The Telegraph that the refusal to allow the entry of food and medicines contravenes international law.
“The UN must assume its responsibility to protect the people of Venezuela,” he said. “The International Criminal Court has the power to take preventative measures and that´s what we´d like to see.”
Mr Maduro has said repeatedly that the arrival of humanitarian aid would be the start of a US-led invasion, insisting that “no one will enter, not one invading soldier.”
Mr Marquez denied that the Venezuelan opposition hoped to provoke military intervention, but he said he was pessimistic about the chances of a peaceful solution.
“I don’t see how negotiations will work,” he said. “They will have to use force to get the aid in.