Venezuelan president Nicolas Maduro has launched what he claims is the biggest military drills in the country's history.

Maduro is facing a battle to maintain power after opposition leader Juan Guaido was recognised by some 50 countries as interim president.

But the defiant 56-year-old leader insisted the nation 'must prepare to defend its sovereignty, territorial integrity and independence' as he kick-started another round of military exercises at Guaicaipuro Fort in Miranda State.

Maduro posted a series of pictures on Twitter showing large crowds of men in military fatigues and tanks rumbling over dusty terrain.

Venezuelan president Nicolas Maduro has launched what he claims is the biggest military drills in Venezuela's history. Pictures and footage on his Twitter account show large numbers of cheering men in army fatigues as well as military vehicles

Maduro, pictured yesterday at the launch of new military drills, is facing a battle to maintain power in the country after opposition leader Juan Guaido was recognised by some 50 countries as interim president

The defiant 56-year-old leader has insisted the nation 'must prepare to defend its sovereignty, territorial integrity and independence' as he kick-started another round of military exercises at Guaicaipuro Fort in Miranda State

He was also seen inspecting weapons in front of cheering soldiers. Venezuela's military announced it had started conducting exercises to 'reinforce the country's defensive capacity.'

According to RT, Maduro said the drills - running until February 15 - were the 'most important' in the country's history and would become the largest it had ever held.

'We must prepare to defend [Venezuela's] sovereignty, territorial integrity, independence,' he said.

On the same day, opposition leader Juan Guaido, recognised by some 50 countries as Venezuela's interim president, warned the military that blocking humanitarian aid from entering the country was a 'crime against humanity.'

The warning comes as international aid has taken centre stage in a test of wills between Guaido and Maduro in which Venezuela's armed forces are seen as the pivotal player.

Maduro posted a series of pictures on Twitter showing large crowds of men in military fatigues and tanks rumbling over dusty terrain

Maduro is said to have claimed that the drills - running until February 15 - were the 'most important' in the country's history and would become the largest it had ever held

Medicine and food sent by the United States has been blocked for three days on the border in Cucuta, Colombia after Venezuelan soldiers closed a bridge linking the two countries.

On the Venezuelan side of the border, dozens of doctors protested Sunday demanding the aid be allowed in - including surgeon Jose Luis Mateus de la Riva, who accused Maduro of sinking Venezuelan medicine back to the 'medieval era.'

'There are people responsible for this and the regime should know it,' Guaido said after attending Sunday mass with his wife and 20-month-old baby. 'This a crime against humanity, men of the armed forces.'

Accusing those blocking aid of being 'almost genocidal,' he likewise warned that the military would be held responsible for the deaths of protesters - and reaffirmed his call for a mass march on Tuesday in memory of the estimated 40 people killed in disturbances since January 21.

Maduro was also seen inspecting weapons in front of cheering soldiers. Venezuela's military announced it had started conducting exercises to 'reinforce the country's defensive capacity'

It comes as international aid has taken centre stage in a test of wills between Guaido and Maduro in which Venezuela's armed forces are seen as the pivotal player

Guaido has offered amnesty for any members of the armed forces who disavows Maduro - but the military leadership still publicly backs the president.

Maduro has rejected humanitarian aid as a US ploy to intervene in Venezuela, calling the deployment of aid a 'political show' and blaming US sanctions for the country's widespread shortages of food and medicine.

Guaido countered that the regime was refusing to acknowledge a 'crisis that they themselves generated,' while Venezuelans were working to deal with the humanitarian emergency.

Speaking to AFP Friday, Guaido vowed to do 'whatever necessary' to 'stop the usurpation' of power and 'save lives' - without ruling out the possibility of authorizing foreign intervention.

And on Sunday, he said hundreds of volunteers had signed up over the weekend to help bring aid into Venezuela - with further shipments set to arrive in neighboring Brazil and on a Caribbean island.

Suffering the worst crisis of its modern history, Venezuelans have had to grapple with life-threatening scarcities amid eye-popping levels of hyperinflation that have rendered salaries and savings worthless.

Venezuela's President Nicolas Maduro inspects a rocket as he attends a military exercise in Charallave yesterday

An officer is pictured speaking to Maduro at the launch of the military exercises at Fort Guaicaipuro in Miranda state

According to the United Nations, some 2.3 million Venezuelans have fled the country since 2015.

But Guaido on Sunday reiterated that he would not negotiate with Maduro - as he believes Maduro would use such talks to buy himself time.

'Democracy is closer than ever before, the future is ours,' he said.

An international Contact Group, made up of European and Latin American countries, called for snap presidential elections following a meeting in Montevideo this week.

But Maduro, who has asked Pope Francis to act as a mediator, rejected what he said was 'bias' by the group.

Last week Maduro also rejected a call by European Union countries to hold elections, prompting them to recognize Guaido.

Guaido, the 35 year-old head of the opposition-controlled National Assembly, stunned Venezuela in January by declaring himself interim president after the legislature declared Maduro a 'usurper' following his May 2018 reelection in a vote disputed by the opposition and international community.