Cucuta, Colombia (CNN) Two US trucks carrying food and medical supplies arrived at Venezuela's border this afternoon, according to a US official in the Colombian border town of Cucuta. But it is not clear when or whether the aid will reach people inside the country.

The government of embattled Venezuelan President Nicolas Maduro has blocked aid deliveries amid rising tensions over opposition plans to bring humanitarian aid into the country.

Venezuela's opposition leader and self-declared president, Juan Guaido, last week named Cucuta as one of three collection points for the delivery of international aid.

His move ramped up tensions with Maduro's government even as many in Venezuela remain in desperate need of such supplies.

Maduro has rejected the international aid, saying: "We are not beggars."

On Friday he tweeted: "The humanitarian aid is a show to humiliate us and is intended to justify military aggression; a macabre plan which does not hide the robbery of more than $10 billion from our nation by the United States. If they want to help, they must stop the blockade, the persecution, and the aggression against Venezuela."

Aid route blocked

Guaido said Thursday he was confident his efforts to bring humanitarian aid into the country would work out.

"We will succeed in letting the humanitarian aid in, because it's about saving lives," Guaido posted on his official Twitter feed. "While we work every day to reach the delivery of humanitarian aid, they insist in siphoning the medicines and food from those who urgently need it."

Colombian officials and a CNN photojournalist at the scene confirmed the presence of the blockade, which would effectively prevent humanitarian aid from reaching Venezuela via this route.

An aerial view of the Tienditas Bridge, on the border between Cucuta, Colombia and Tachira, Venezuela, after it was blocked with containers.

Images show an orange oil tanker and two large blue containers positioned midway across the three-lane Tienditas Bridge, which connects Cucuta with San Antonio city in Tachira State in western Venezuela.

Juan Caicedo, a spokesperson from Migration Colombia, Colombia's Ministry of Immigration and Immigration Control, said the Venezuelan military put the blockade into place Tuesday afternoon, adding that there are cameras monitoring activity on the bridge.

US: Open the bridge

It's possible the Venezuelan government fears aid crossing the border could be used as cover for an invasion to depose Maduro.

Guaido called Wednesday on the conscience of Venezuela's military -- which has so far been loyal to the government -- to permit aid into the country from Colombia, which is run by a right-wing government critical of Maduro.

"Brother, let the aid in. Do not stop it," he said, appealing to members of the country's armed forces while speaking at a meeting with farmers in Caracas. "The end of the usurpation will be the end of hunger," he added, as he called for Venezuelans to reject the Maduro government.

US Secretary of State Mike Pompeo also urged Venezuela to open the bridge, tweeting that "the Maduro regime must let the aid reach the starving people."

The Venezuelan people desperately need humanitarian aid. The U.S. & 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 pic.twitter.com/L4ysYJaM6H — Secretary Pompeo (@SecPompeo) February 6, 2019

Appeal for loyalty

Maduro has faced intense pressure since Guaido declared himself acting president on January 23, invoking a constitutional rule to open a rare challenge to Maduro's presidency.

Guaido, a previously largely unknown opposition leader, has been recognized by Australia, Canada, a group of major European nations , a number of Latin American countries and the United States, which have upped sanctions on the country.

JUST WATCHED CNN speaks to Juan Guaidó's family as history unfolds Replay More Videos ... MUST WATCH CNN speaks to Juan Guaidó's family as history unfolds 02:52

Venezuela's Foreign Ministry has denounced any international support for Guaido, suggesting that European governments were acting as part of a US-led effort to topple Maduro, who has showed no signs of relinquishing power.

On Thursday, Venezuelan Minister of Communications Jorge Rodriguez claimed he presented "proof" of what he called a US-backed coup attempt against Maduro's government in January.

Speaking live on television from the Miraflores Presidential Palace in Caracas, Rodriguez showed two alleged filmed confessions by military men who were implicated in the plot and were later arrested by security forces.

CNN could not independently verify the authenticity of the video.

The two men described a plot headed by opposition figure Julio Borges, a former president of Venezuela's National Assembly living in Bogota.

According to Rodriguez's reconstruction of the facts, Borges and other opposition leaders, with the help of the CIA, were organizing a military uprising in Caracas that was discovered and blocked by Venezuelan security forces on January 21.

Maduro on Wednesday hit back at a tweet by US national security adviser John Bolton that said "any Venezuelan senior military officer that stands for democracy and recognizes the constitutional government of President Juan Guaido" would not face US sanctions.

Speaking during military exercises, Maduro called for the Venezuelan military to remain loyal and ordered the armed forces to defend Venezulean territory.

"Is John Bolton Venezuela's military chief? Listen well John Bolton, here is the response of the armed forces to your so-called coup-makers. Let's say our slogan loudly, "Loyal Always, Traitors Never" so it can be heard in Washington," he said.

Maduro also welcomed a meeting of the International Contact Group on Venezuela in the Uruguayan capital, Montevideo on Thursday saying: "We are ready and prepared to participate in a process of sovereign, constitutional dialogue."

The contact group includes Bolivia, Costa Rica, Ecuador, France, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, the United Kingdom and co-host Uruguay.

International aid pledges

Guaido identified the three collection points for international humanitarian aid as the Brazil-Venezuela border, an as-of-yet unidentified Caribbean island, and Cucuta. However, it remains unclear if aid will be allowed in by any of these routes.

On Monday, Canada hosted a meeting of the Lima Group regional bloc to discuss how the international community can further help the people of Venezuela, including through immediate humanitarian assistance.

Opening a session in Ottawa, Prime Minister Justin Trudeau announced a contribution of 53 million Canadian dollars ($40.4 million) in aid to Venezuela.

German Foreign Minister Heiko Maas also said Germany had earmarked €5 million ($5.72 million) worth of assistance for Venezuela. Later on Monday, Guaido said Germany had pledged €6 million ($6.86 million.)

USAID has begun packaging pallets of foodstuffs after Bolton's announcement last week that it would send humanitarian aid.

Guaido called the situation "an emergency ... a crisis," on Monday and said humanitarian aid would begin to flow into Venezuela in the coming days, defying Maduro's repeated refusal of assistance in the face of food and medicine shortages.

He outlined the move as part of a plan to push the military into cooperating with the opposition.