STATE DEPARTMENT - Officials in Washington and Moscow on Friday expressed a desire to extend their week-old cease-fire pact for Syria and confirmed aid deliveries had not yet begun, but agreed on little else concerning the tenuous situation in the war-torn country.

Forty trucks carrying desperately needed relief for the divided city of Aleppo were idling at a special customs checkpoint at the Turkish border, and the U.S. blamed the Syrian government for the holdup.

"Those trucks should be going in and that aid should be getting delivered with or without the arrangement that was arrived at in Geneva," State Department spokesman John Kirby said. "It is the [Syrian] regime that is blocking the movement."

U.N. officials said conditions were not yet safe for the vehicles to cross into Syria.

In this photo provided by the Syrian Civil Defense In this photo provided by the Syrian Civil Defense White Helmets, men stand in rubble after airstrikes hit eastern Aleppo, Syria, Sept. 9, 2016. In this photo provided by the Syrian Civil Defense White Helmets, men stand in rubble after airstrikes hit eastern Aleppo, Syria, Sept. 9, 2016.

'Whole world is watching'

"We know that there's at least a quarter of a million people in eastern Aleppo who are ... in need of some kind of aid," said Jens Laerke, a spokesman for the U.N. humanitarian office. "We are as ready to go as we can possibly be. ... It's highly frustrating. We know the whole world is watching."

Syrian government troops had withdrawn from Aleppo but were then fired upon by rebels, prompting the soldiers to return to their previous positions, according to Russian officials, who also blamed Washington for not using its influence to quell cease-fire violations by rebel groups.

The Americans have a different view, with Secretary of State John Kerry expressing concern in a Friday phone call to Russian Foreign Minister Sergei Lavrov "about the repeated and unacceptable delays of humanitarian aid," according to a State Department statement.

Meanwhile, in New York, the U.N. Security Council canceled a meeting on Syria that was scheduled for late Friday. The cancellation came at the request of the U.S. and Russia.

Under the cease-fire agreement Kerry and Lavrov announced in Geneva a week ago, hostilities should have paused Monday (the start of the Muslim holiday of Eid al-Adha) to clear the way for humanitarian aid to flow unhindered into Syria. Starting next Monday — if those conditions are met — the United States and Russia are to begin joint coordination of airstrikes against the Islamic State and Jabhat Fatah al-Sham, formerly known as the al-Nusra Front, which are not parties to the truce.

Commercial Turkish trucks wait to cross to Syria n Commercial Turkish trucks wait to cross to Syria near the Cilvegozu border gate, located opposite the Syrian commercial crossing point Bab al-Hawa in Reyhanli, Hatay province, Turkey, Sept. 16, 2016. Commercial Turkish trucks wait to cross to Syria near the Cilvegozu border gate, located opposite the Syrian commercial crossing point Bab al-Hawa in Reyhanli, Hatay province, Turkey, Sept. 16, 2016.

Delays could threaten agreement

The White House indicated Friday that the next phase of the deal would not move forward until the aid was moving freely.

In a statement, the White House said President Obama emphasized to his National Security Council that "the United States will not proceed with the next steps in the arrangement with Russia until we see seven continuous days of reduced violence and sustained humanitarian access."

If the deal does falter, Kirby told reporters "we're back to regrettably where we have so long been: innocent civilians being barrel-bombed and gassed."

Over the last several days, there have been acts of violence "committed by all sides," according to Kirby.

The Syrian Observatory for Human Rights said U.S. special forces — believed to be only five or six personnel — entered the Syrian town of al-Rai on Friday to coordinate airstrikes against Islamic State militants.

Video posted on the internet purportedly of those forces leaving the town showed fighters of the U.S.-backed Free Syrian Army chanting anti-American slogans and hurling insults, adding that they would not fight alongside the Americans.

A rebel fighter walks by damaged buildings near Ca A rebel fighter walks by damaged buildings near Castello road in Aleppo, Syria, Sept. 16, 2016. A rebel fighter walks by damaged buildings near Castello road in Aleppo, Syria, Sept. 16, 2016.

U.S. officials on Friday would not confirm the authenticity of the video. But if the slurs were uttered by supposed allies in the fight against IS, it is "unacceptable and reprehensible," Kirby told reporters.

The U.S. Defense Department has previously acknowledged its special operations teams are accompanying Turkish and some Syrian opposition armed personnel in the area and further east, near Jarablus.

Meanwhile, Turkish-backed rebels, according to Ankara, have been involved in deadly clashes with IS in northern Syria with the support of Turkish warplanes and tanks.

Political transition

It is hoped that the truce forged by the United States and Russia will clear the way for negotiations about a political transition in Syria. But rebel leaders say they expect the cease-fire to collapse and do not believe Syrian President Bashar al-Assad — or his foreign backers, Russia and Iran — want to negotiate a political settlement.

"The armed groups on the ground are still discussing what they should do about the cease-fire," General Salim Idris, former chief of the staff of the Free Syrian Army, told VOA.