The five-day truce initiated by a Saudi-led coalition that has bombarded the Iran-backed rebels for more than six weeks expires late tomorrow, and Riyadh has already warned it was "ready to act" against any ceasefire violations.
In the latest violence, at least 12 civilians were killed when the Shiite Huthi rebels shelled several neighbourhoods in Yemen's third city of Taez, an official there told AFP.
Fighting overnight killed 26 rebels - Huthis backed by militiamen loyal to former president Ali Abdullah Saleh - as well as 14 pro-government forces, military sources said.
It says more than 1,500 people have died in the conflict since late March.
More From This Section
Some aid has begun to trickle into Yemen since the pause in fighting, but residents of areas where clashes persist complain they remain without the most basic supplies.
The fighting in Taez overnight forced many to flee to neighbouring countryside.
"Humanitarian aid hasn't reached Taez, where we haven't received fuel, food or medical equipment," the government official in the city said.
UN coordinator Johannes van der Klaauw warned that the inspections, introduced under an arms embargo slapped on the Huthi rebels last month, were hampering access for vital goods.
"The arms embargo and its inspection regime results in commercial goods, be it by air or by ship, no longer reaching the country," he told journalists in Geneva via a conference call from Yemen.
The UN Security Council hit the Huthis with the embargo after they captured the capital Sanaa and advanced on the southern city of Aden, forcing President Abedrabbo Mansour Hadi into exile.
Saudi Foreign Minister Adel al-Jubeir accused the Huthis of repeatedly violating ceasefire terms.
"We are hoping that the Huthis will abide by the terms of the ceasefire and stop their aggressive behaviour if they want the ceasefire to hold," he said during a US summit with Gulf allies this week.