Venezuelan doctors have called on the military to unblock the Tienditas International Bridge so humanitarian aid can reenter the country.
They protested on the Colombian side of the border to avoid repercussions at a time of huge political tension.
Opposition leader Juan Guaidó has proclaimed himself interim president after claiming Nicholas Maduro's presidency is illegitimate.
The US has imposed harsh sanctions on the country's oil exports.
Jens Laerke, a spokesman for the UN Office for the Coordination of Humanitarian Affairs, is committed to delivering aid.

Iran says it is reviewing US proposal to end war
UN Human Rights Council adopts resolution condemning Iranian attacks
Russian attacks kill two in Ukraine's Kharkiv
Kuwait foils terror plot targeting state leaders
Iran rejects Trump's talk of negotiation as Israel and Iran launch airstrikes
Cyprus has opened discussion with UK over its bases, president says
Netanyahu seeks to avoid snap vote as Iran war gives no boost in polls
Luxury Paris hotel near Elysee reopens after fire forces brief closure
