Yemen's Houthi rebels say they will decide Friday whether the government is serious about peace talks.
"We have no problem holding talks with the other side. We will judge whether the Stockholm talks are serious or not tomorrow," a rebel spokesman told an Arabic language television network.
The U.N.-sponsored talks opened Thursday in Rimbo, Sweden, north of Stockholm.
WATCH: UN Envoy: Success of Yemen Talks Depends on Warring Sides
These are the first talks between the Iranian-backed Houthi rebels and the Saudi-supported Yemeni government since 2016. They are aimed at moving toward a political settlement of the 4-year-old war.
U.N. envoy Martin Griffiths reported some progress after the first full day of talks Thursday when both sides agreed on a prisoner swap.
"I'm also pleased to announce the signing of an agreement on the exchange of prisoners, detainees, the missing, the forcibly detained, and individuals put under house arrest," Griffiths said. "It will allow thousands of families to be reunited and it is product of very effective, active work from both delegations."
Griffiths urged both sides to "work in good faith ... to deliver a message of peace."
But one of the main hurdles will be the port city of Hodeida, where nearly all food and humanitarian aid deliveries are made.
The rebels control the city. The Saudi-led coalition trying to drive the Houthis out of Yemen say they receive Iranian-made weapons through the port — a charge Iran denies.
Much of the recent fighting has been in and around the city. The Yemeni government is demanding the rebels withdraw. They refuse.
U.N. and humanitarian groups say a dangerous disruption of food and medical deliveries through the port will make a dire humanitarian situation even worse.
Nearly 80 percent of Yemeni civilians lack food, medicine, and fresh water and the entire country is on the edge of famine.
Saudi-led airstrikes against the rebels are compounding the misery — wiping out entire neighborhoods and destroying hospitals. A Saudi missile strike on a busload of children in August killed 40. The coalition called the attack "a mistake."
More than 10,000 people have been killed since the fighting broke out in 2014 when the rebels seized the capital of Sanaa, forcing the government to flee to temporary exile in Saudi Arabia.
The U.S. Senate is considering a resolution demanding the Trump administration cut off all military aid to the Saudi coalition.