A ceasefire billed as the "last chance" to halt Syria's five-year war collapsed on Monday night as air strikes battered Aleppo and a UN aid convoy was hit near the city.

AFP takes a look at why it failed, what took place during the week, and what could happen next.

Why did the truce collapse?

The deal came into effect on September 12, after marathon talks in Geneva between US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov.

Syria's military declared the week-long truce over on Monday evening, accusing rebels of more than 300 violations.

"We have not had seven days of calm and of delivery of humanitarian goods," Kerry told reporters in New York after the army's announcement.

Russia said rebel breaches made it "pointless" for Syrian troops to uphold the ceasefire, but that it could resume if "terrorists" stopped their attacks.

The deal faced major obstacles from the start.

While Syria's army had announced it would halt fighting, rebel groups never formally signed on, citing reservations about monitoring mechanisms.

The text of the agreement was not made public, and neither the UN Security Council nor the main opposition umbrella group, the High Negotiations Committee, saw the full deal.

Rebels and regime forces traded accusations over violations all week.

The deal came under growing strain at the weekend after fresh strikes on Aleppo and a US-led air raid in the country's east that killed dozens of Syrian troops.

Russian ambassador Vitaly Churkin called the strike a "bad omen" for the US-Russia agreement.

There was also little progress on aid, a key part of the agreement that could have been used to build much-needed trust among Syria's warring sides.

Hours after Syria's army declared the truce over, a deadly raid hit a joint United Nations, Red Cross, and Red Crescent convoy delivering aid to the town of Orum al-Kubra in Aleppo province.

What happened in the first week?

After the ceasefire came into force, activists and AFP correspondents around the country initially reported relative calm on major battlefronts.

Residents in divided Aleppo said air strikes and shelling, common before the truce, were not heard in the first few days.

But fighting began building up later in the week, particularly in the central provinces of Hama and Homs, Latakia in the west, and the rebel stronghold of Eastern Ghouta near Damascus.

The Syrian Observatory for Human Rights, a British-based monitor, said in total 27 civilians were killed during the week in areas where the truce applied -- far fewer than usual.

Only three known aid deliveries took place during the ceasefire: to Moadamiyet al-Sham near Damascus on Sunday, and Orum al-Kubra and the central town of Talbisseh on Monday.

Convoys carrying aid for besieged civilians in eastern parts of Aleppo city never managed to cross over the Turkish-Syrian border.

What happens next?

Key players including the United States and Russia are to meet in New York on Tuesday in an effort to salvage the peace process, before a UN Security Council meeting on Syria the next day.

But after the latest developments, hopes of a lasting deal are slim.

"The problem with failed ceasefires and failed diplomacy is that they come at a political cost," said Emile Hokayem from the International Institute for Strategic Studies.

"A failed ceasefire means that the other two prongs of the approach (humanitarian access and political talks) are doomed," Hokayem told AFP.

A landmark truce agreed in February -- also by the US and Russia -- fizzled out after weeks of relative quiet, and UN-brokered peace talks have yet to resume.

Now, according to Hokayem, "the US and the UN have less credibility with rebel groups, who out of despair, spite and radicalisation are more willing to flout international humanitarian law or international calls for talks and de-escalation."

But he said "indefatigable" Kerry would try to reach a new deal, despite indications violence will escalate further.