Fighting has continued in the rebel-held Eastern Ghouta area in Syria, despite a five-hour "pause" ordered by the government's ally Russia.

Activists said the government carried out a number air and artillery strikes, while state media accused rebels of shelling a "humanitarian corridor" meant to allow civilians to leave.

As a result, there were no UN aid deliveries or medical evacuations.

Earlier, the US called on Russia to use its influence to secure a 30-day truce.

The UN Security Council unanimously passed a resolution demanding a nationwide cessation of hostilities on Saturday, but it did not give a specific start date.

What is happening on the ground?

A spokesman for the UN Office for the Co-ordination of Humanitarian Affairs (OCHA) said it had received reports that fighting continued after the Russian-ordered pause began on Tuesday morning.

"Clearly, the situation on the ground is not such that convoys can go in or medical evacuations can go out," Jens Laerke told reporters in Geneva.

The Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group, said the situation in the Eastern Ghouta had been relatively calm overnight.

But it reported that in the first two hours of the Russian-ordered "humanitarian pause", a number of shells hit the towns of Douma, Harasta and Misraba.

Later, it reported air strikes, including the dropping of two barrel bombs on the town of al-Shifuniya, and rocketfire in the enclave.

The Syrian Civil Defence, whose volunteer rescue workers are widely known as the White Helmets, said one person was killed in Douma by shellfire. But the Syrian Observatory said the attack happened before the pause began.

The Syrian state news agency, Sana, reported that "terrorists" had shelled the route of the humanitarian corridor leading to the government-controlled al-Wafideen Camp, which is north-east of Douma, and were using "human shields".

At least 568 civilians have been killed in government air and artillery strikes on the enclave over the past nine days, according to the Syrian Observatory.

Russia said the pause in bombardment would run from 09:00 until 14:00 local time (07:00-12:00 GMT) daily.

The Syrian Red Crescent would help set up the humanitarian corridor and residents would be informed about how to leave via leaflets, text messages and videos, it added.

Buses and ambulances will be waiting at a crossing to evacuate the sick and wounded.

"Five hours is better than no hours, but we would like to see an end to all hostilities extended by 30 days, as stipulated by the Security Council," UN spokesman Stephane Dujarric told AFP news agency.

Meanwhile, UK Foreign Secretary Boris Johnson said it should consider carrying out air strikes in Syria if there was evidence that chemical weapons had been used.

"If we know that it's happened, and we can demonstrate it, and if there is a proposal for action where the UK could be useful, then I think we should seriously consider it," he told the BBC.

His comments came two days after a reported chlorine attack on the Eastern Ghouta. The Syrian government has denied using chemical weapons, but UN experts are confident it has used chlorine and the nerve agent in Sarin in the past.

Will the pause allow aid to be brought in?

Aid agencies say they need to be able to trust in the ceasefire actually taking place on the ground before sending in relief workers and vehicles.

Dr Mohamad Katoub a Turkey-based doctor with the Syrian American Medical Society (SAMS), which supports hospitals in the Eastern Ghouta, told the BBC: "We don't believe that this truce will bring any benefits for the civilians inside Eastern Ghouta. Five hours is not enough to do anything."

"This truce doesn't mean that we NGOs there will have any access to bring any items inside Eastern Ghouta.

"The only access is the UN inter-agency convoys. Their access there is very limited due to the restrictions from the Syrian government.

"Only 10 convoys entered Ghouta in 14 months and those convoys brought less than 10% of the needs."

Will people be able to get out during the pause?

Al-Wafideen has long been the formal point for people to enter and exit the Eastern Ghouta.

But Reach Initiative, which is monitoring the humanitarian situation in the enclave, said earlier this month that less than 10% of the enclave's population - made up of public sector employees and males over 40 - were permitted to leave. Women and children reportedly continued to be forbidden by rebel groups from leaving for security reasons, it added.

The organisation said people attempting to leave the area faced sniper fire, landmines, shelling, verbal and physical harassment, detention, and, in the case of women, sexual harassment, humiliating inspections and beatings.

A journalist for the pro-opposition Ghouta Media Center who lives in Douma told the BBC that it was too dangerous to venture outside, let alone try to reach al-Wafideen.

"I went outside but only for a while," Firas Abdullah said. "After half a minute of this ceasefire, shells were dropped. Even if anyone tries to leave, he will be shot by the snipers of the regime checkpoint."

Is this the same as the UN's proposed truce?

No. The Security Council resolution demanded that "all parties cease hostilities without delay for at least 30 consecutive days" to allow humanitarian aid deliveries and medical evacuations of critically ill people.

UN Secretary-General Antonio Guterres said on Monday that the resolution needed to be implemented immediately, warning: "Eastern Ghouta cannot wait. It's high time to stop this hell on Earth."

But Russian Foreign Minister Sergei Lavrov told reporters that the UN-mandated truce would "start when all sides of the conflict agree on how to introduce it".

The jihadist groups Islamic State (IS) and al-Qaeda are excluded, as well as the major Islamist rebel factions Ahrar al-Sham and Jaysh al-Islam.

Mr Lavrov called them "partners of al-Nusra Front" - the name of a former al-Qaeda affiliate whose latest incarnation is an alliance of jihadists called Hayat Tahrir al-Sham (HTS). It has a small presence in the Eastern Ghouta.