U.N. humanitarian aid delivery from Turkey to rebel-held northwestern Syria is tightly monitored and remains critical, Secretary-General Antonio Guterres says in a report that could be key to keeping the effort going.

“Despite challenges, humanitarian aid is delivered, and services are provided, in a principled and transparent manner throughout the country,” Guterres said in the report, which was circulated internally within the United Nations and obtained by The Associated Press on Wednesday.

The report follows tense Security Council negotiations last summer over continuing the cross-border aid deliveries through the sole route where they are currently allowed — the Bab al-Hawa crossing to Idlib province, which is home to 3 million people and Syria’s last major rebel stronghold after a decade of civil war.

Syria, which isn’t a council member, called the cross-border convoys politicized and unnecessary. Close ally Russia, which last year used its veto threat in the council to end deliveries through three other crossings, argued this summer that humanitarian supplies could and should instead be sent across conflict lines within Syria to reinforce the government’s sovereignty over the entire country.

U.N. officials, the United States, Europeans and others said the cross-border deliveries remained crucial, warning that stopping them could bring devastating consequences for a million or more Syrians.

A day before the authorization was to run out, the council struck a compromise in July.

Members agreed to keep the aid flowing through Bab al-Hawa until Jan. 10, 2022, with an automatic six-month extension if Guterres issued a “substantive report” on the operation’s “transparency” and progress on delivering aid across Syria’s internal front lines.

Hence the new report, in which Guterres details how cross-border shipments are checked and tracked. He calls the initiative “one of the most closely monitored operations in the world.”

He says “clear progress has been made” on delivering aid across internal conflict lines, but adds that even if the U.N. can fully carry out a six-month plan that it made this fall, those convoys won’t be able to match the shipments coming across the border.

“The cross-border operation remains an essential part of the humanitarian response and will continue to do so as long as needs cannot be addressed at the same scope and scale through any other modality,” he wrote.

A request for comment was sent to Russia’s U.N. mission Wednesday evening.

AP