CNN  — 

US national security adviser John Bolton has canceled his trip to South Korea next week, even as preparations ramp up for a second summit between President Donald Trump and North Korean leader Kim Jong Un.

“Ambassador Bolton has canceled his travel to the Republic of Korea to focus on events in Venezuela,” National Security Council spokesman Garrett Marquis said in a statement. Bolton is still planning to travel to Hanoi, Vietnam, with President Trump for the North Korea summit, which starts February 27, he said.

Bolton, who famously flashed reporters a yellow notepad with the scrawled words “5,000 troops to Colombia” during a briefing about Venezuela last month, won’t be the only high-ranking US official focusing on the divided, oil-rich country.

Monday, US Vice President Mike Pence is expected to travel to Colombia in an effort to pressure embattled Venezuelan President Nicolas Maduro to step down. He plans to meet with the Lima Group, a regional bloc of nations, and deliver remarks to address the “tragic humanitarian and security crises unfolding in Venezuela and ongoing US efforts to deliver aid to the country.”

And Elliott Abrams, the recently appointed US Special Representative for Venezuela, arrived in the Colombian border town of Cucuta Thursday.

Their plans coincide with a heightening of tensions in Venezuela over aid deliveries: Late on Friday night, Venezuelan Vice President Delcy Rodriguez announced a “total temporary closure” of the Colombian borde – just hours ahead of the deadline for food and medical supplies to finally enter the country set by self-declared acting president Juan Guaido.

Venezuelan civilian volunteers had been preparing to carry aid across the border from neighboring Colombia, where foreign shipments of food and medical supplies have been waiting for weeks.

The Maduro regime has already closed its borders with Brazil and Curacao, where more aid is stockpiled. At least two people died in a skirmish with the Venezuelan military at the Brazilian border over aid deliveries Friday.

Guaido in Colombia

The Venezuelan military is still largely loyal to Maduro and is expected to enforce his vow to block aid deliveries. But Friday, Guaido made the surprise announcement that the military had helped him to defy a travel ban, assisting his border crossing from Venezuela into the Colombian city of Cucuta.

“The question is, how did we get here today to Colombia when they blocked the airspace? When they blocked all types of maritime customs, they put obstacles on the roads,” Guaido said, adding: “We are here precisely because the armed forces also participated in this process.”

He did not clarify the nature of the assistance from the armed forces, and has not specified how or when he intends to return to Venezuela.

Guaido made his comments at a news conference alongside Colombian President Ivan Duque, Chilean President Sebastian Pinera, Paraguayan President Mario Abdo Benitez, and Organization of American States Secretary-General Luis Almagro. Like Trump, all have recognized Guaido as the legitimate head of Venezuela.

Jorge Perez, Isa Soares and Julia Jones in Venezuela, and Taylor Barnes and Radina Gigova in Atlanta, contributed to this report.