Syrian officials in Damascus said the decision, seven days after the 7.8 magnitude earthquake killed thousands, shows their commitment to supporting victims on both sides of the front line.
The increased flow of help was desperately needed. But some critics say the deal is also a political victory for embattled Syrian President Bashar Assad, who permitted the U.N. to open new crossings and gave the impression that he ultimately called the shots on territory under opposition forces.
The U.N. is normally authorized to deliver aid from Turkey to northwest Syria _ an area already devastated by 12 years of conflict _ through only one border crossing, Bab al-Hawa. Renewing that authorization is a regular battle at the Security Council, where Assad's ally, Russia, has advocated for all aid to be routed through Damascus.
The delay in opening new crossings stalled immediate relief and search and rescue efforts when the "time for effective search and rescue is tragically running out,'' the International Rescue Committee said in statement.
Asked why it took so long to increase aid access to the northwest, Syria's U.N. ambassador Bassam Sabbagh told reporters, "Why are you asking me? We don't control these borders.''
The move by Damascus to open additional border crossings a week after the quake was more political than humanitarian, said Joseph Daher, a Swiss-Syrian researcher and professor at the European University Institute in Florence, Italy.
"It's a way for the regime to reaffirm its sovereignty, its centrality, and to instrumentalize this tragedy for its own political purposes,'' he said.
Before the deal with Damascus, advocates had been pushing for the Security Council to vote to permanently open more border crossings to aid deliveries _ a move almost certain to be vetoed by Russia.
Others argue that no Security Council resolution is needed for the U.N. to send aid across borders in an emergency. Daher pointed out that the U.N. had airdropped aid into the Syrian city of Deir Ezzor when it was besieged by Islamic State militants.
Russia's foreign ministry Tuesday issued a statement condemning attempts to "push through'' a permanent expansion of the authorized crossings.
It said Western nations "continue to strangle" Syria with sanctions that it said have caused a fuel crisis and "prohibited the import of vital goods and equipment.''
The United States, United Kingdom and European Union have imposed sanctions on Assad and oppose funneling aid to the northwest through his government, believing it would divert aid to its supporters.
A State Department spokesperson told the AP Tuesday that Washington will push for a U.N. resolution authorizing additional crossings as soon as possible. The U.S. last week issued a license to allow earthquake-related relief to bypass sanctions.
The U.K. welcomed the temporary opening of new crossings, but said "sufficient access needs to be secured in the longer term.''
When the earthquake hit, the U.N. could not immediately access Bab al-Hawa because of infrastructure damage, leaving the shattered enclave without significant aid for 72 hours.
Northwest Syria's civil defense organization, the White Helmets, said the delay in aid and the U.N.'s failure to take unorthodox measures those first few days cost lives, as they struggled with limited equipment and manpower to rescue thousands of people trapped under the rubble.
The U.N. tried to send a delivery of aid to rebel-held Idlib through government-held territory on Sunday, but the shipment was halted after Hayat Tahrir al-Sham, the al-Qaida-linked organization that controls the area, refused to accept aid coming from Assad-controlled areas.
That standoff was "good politically ... for both sides,'' Daher said, allowing the rebels "to say, `I'm not collaborating with the regime' and for the regime to say, 'Look, we tried to send assistance.''
Meanwhile, cargo planes loaded with aid have reached government-held territory, including from the United Arab Emirates, Saudi Arabia, Jordan and Egypt _ countries that once shunned Assad and have slowly been reviving ties in recent years.
Agreeing to the temporary additional crossings is to Assad's political advantage,says Charles Lister, Director of the Syria program at Washington-based think thank Middle East Institute.
The decision "goes against everything that the regime has publicly stood by for the past 10-plus years when it comes to cross border aid delivery,'' Lister said, referring to Syria and Russia's attempts at ending the U.N. cross-border aid mechanism.
But with the deal, the Syrian government "knows it has proved to the world that the United Nations is unwilling to do anything in Syria without the regime's permission.''
Saria Akkad, partnerships and advocacy manager with the Ataa Humanitarian Relief Association, which works in Turkey and northwest Syria, said that Syrians like him now feel that their advocacy to the U.N. was pointless. "We should maybe go back to Assad, we should discuss with the person who killed his people, how he can support the people in northwest Syria,`` he said.
Lister said the current crisis has allowed Assad to "bait the international community into normalization", though he doesn't expect a total end of his political isolation without major shifts form Washington and London.
Syrian officials have urged the U.N. to fund reconstruction, and Lister believes that this, in addition to the lifting of Western sanctions, is what Damascus hopes to get.
The temporary authorization ends in three months, around the time negotiations take place before the U.N. Security Council meets in July to review the cross-border resolution. Lister believes that Assad's agreement with the U.N. could allow him to ask for more in return in exchange for allowing the resolution to continue without a Russian veto.
"I think what we frankly saw yesterday was the U.N. politicizing aid delivery by going to the regime to secure access to a border crossing they don't have control over,'' he said. "It put all its eggs into the regime's basket.''