The first commercial flight due to take off from Yemen’s capital in six years was canceled on Sunday.

Moammar al-Iryani, the information minister of the country’s internationally-recognized government, said flight was canceled as some passengers had been issued passports by the Iran-backed Houthi militia.

While 104 passengers bore government-approved passports, 60 had “unreliable” passports issued by the Houthis, al-Iryani said in a tweet.

The Yemeni government announced in March 2017 that it doesn't recognize documents issued by the Houthis.

As part of a truce between the warring sides that began at the beginning of the holy month of Ramadan in early April, the two parties agreed to operate two commercial flights a week to and from Sanaa to Jordan and Egypt.

Sunday’s flight was destined to land in Jordan’s capital Amman.

Hans Grundberg, the UN special envoy for Yemen, urged both sides to “work constructively” with the UN to address the challenges that delayed the flight.

“The Truce is meant to benefit civilians including through reducing violence, making fuel available, and improving their freedom of movement to, from and within their country,” he said on Twitter. He did not elaborate.

Along with the flights, the truce also included allowing 18 vessels carrying fuel into the port of Hodeida, which is controlled by the Houthis.

The sides have also yet to convene on a reopening of roads around Taiz and other provinces as part of the truce. The government accused the Houthis of delaying the meeting as they did not send their delegation’s members to the UN envoy's office where the meeting was to be held.

The truce has resulted in a subsiding of ground and air fighting and the Houthis have stopped their cross-border attacks on Saudi Arabia and the United Arab Emirates, another pillar of the anti-Houthi coalition.

Both sides, however, have reported almost daily violations of the cease-fire, especially around the government-held central city of Marib, which the Houthis have attempted to seize for over a year.