Venezuela's opposition leader has called for more forceful multilateral action against Nicolas Maduro's regime as US Secretary Mike Pompeo raised the possibility of more sanctions against the president, saying his "days are numbered". Juan Guaido, president of Venezuela’s National Assembly, made the call after an attempt to move humanitarian aid into the country was blocked with force by Venezuelan troops on Saturday, who killed four civilians. Mr Guaido said he would meet on Monday with officials from other regional countries who are backing his push to remove Mr Maduro before he announced the next steps. He did not specify what the steps could be but said all options were being considered. “I’ve been forced to take a decision: formally propose to the international community that we should have all options open to achieve the liberation of this motherland, which is fighting and will continue to fight,” Mr Guaido tweeted. “Hope has been born to never die, Venezuela.” Mr Pompeo said Washington was considering more sanctions against Mr Maduro's government and that further action would be discussed at Monday's meeting in the Colombian capital Bogota. He said he was confident Mr Maduro's time in office was running out. "Predictions are difficult. Picking exact days is difficult," Mr Pompeo told CNN's <em>State of the Union</em> programme on Sunday. "I'm confident that the Venezuelan people will ensure that Maduro's days are numbered." Mr Guaido is expected to meet US Vice President Mike Pence before the talks in Bogota with the Lima Group, a coalition of a dozen countries in the Americas committed to regime change in Venezuela. The US is among dozens of nations that have recognised Mr Guaido's claim to be Venezuela's interim president until impartial elections can be held. Mr Maduro has received backing from countries such as Russia, Cuba and Turkey. "We're aimed at a singular mission – ensuring the Venezuelan people get the democracy they so richly deserve and the Cubans and the Russians who have been driving this country into the ground for years and years no longer hold sway," Mr Pompeo said. Mr Maduro closed the borders with Brazil, Colombia and Curacao and posted military and pro-government militias near the crossing points and in border towns, to push back and intimidate opposition supporters and volunteers trying to take food and medicine into Venezuela. He insisted that Mr Guaido was using humanitarian aid as an excuse for intervention, while the opposition maintains that it is an attempt to relieve a malnourished and suffering population in Venezuela’s worst economic collapse. Venezuela's military has largely stood by Mr Maduro despite Mr Guaido's offer of an amnesty if they deserted, although 60 members of the armed forces defected along the borders of Colombia and Brazil on Saturday. But lorry loads of humanitarian aid donated by nations backing Mr Guaido’s bid for power remained outside the country and Mr Maduro taunted his rivals in a speech in Caracas. “I am stronger than ever,” he told crowds of supporters. “Standing, ruling our homeland, for now and for many years.” Mr Guaido must now consider his next step with allies and, having crossed into Colombia hours before the attempted aid push, he faces the challenge of returning as Mr Maduro threatens to imprison him for breaching a travel ban. “We saw today a man who doesn’t care about Venezuela, ordering to burn food for the hungry and medicine in front of the sick,” Mr Guaido said. Mr Maduro “has chosen the worst of paths, the path of crime and extermination”, he said. “Venezuela’s military has a choice: embrace democracy, protect civilians, and allow in humanitarian aid; or face even more sanctions and isolation,” US National Security Adviser John Bolton wrote on Twitter. Saturday’s clashes on the Colombian border injured 285 people, mainly with tear gas and “non-conventional arms", said Carlos Trujillo, Colombia’s Foreign Affairs Minister. Thirty-seven people needed treatment in hospital. The push from Colombia began on Friday with a music festival organised by Sir Richard Branson in the border town of Cucuta, which drew more than 300,000. Many stayed and early the next morning began confronting Venezuelan troops on the area’s four international bridges.