A 46-truck convoy carrying humanitarian aid have entered Eastern Ghouta through a government-controlled checkpoint for the first time in nearly a month, but crucial medical supplies have been confiscated by the Syrian military.

Robert Mardini, head of Middle East operations for the International Committee of the Red Cross, said in a tweet on Monday that a convoy carrying desperately needed aid for tens of thousands was on its way to Eastern Ghouta.

The convoy included surgical supplies and medicine, as well as 5,500 food and flour bags enough for 27,500 people.

Ali al-Za'tari, a senior UN official with the convoy, told Reuters news agency it would take "many hours" to offload the aid in the rebel-held enclave, and it might be "well after nightfall" before it could leave Eastern Ghouta.

A World Health Organization official said the government had ordered 70 percent of medical supplies to be stripped out of the convoy, preventing trauma kits, surgical kits, insulin and other vital material from reaching the area.

The ICRC confirmed some medical equipment had been blocked but gave no details.

More than 700 civilians have been killed during an aerial offensive that began on February 18.

The area, home to 400,000 people, has been under siege by the government ever since armed opposition groups took control in mid-2013.

Bombardment on the enclave killed at least 45 civilians on Monday, the Syrian Observatory for Human Rights (SOHR) said.

The UK-based war monitor said at least 19 of the victims died in the town of Hammuriyeh, where barrels bombs were dropped.

The SOHR said the death toll could rise as bodies were being retrieved from the rubble.

Za'tari said he was "not happy" to hear loud shelling near the crossing point into Eastern Ghouta despite an agreement that the aid would be delivered in safety.

"We need to be assured that we will be able to deliver the humanitarian assistance under good conditions," he said.

A 30-day ceasefire unanimously voted for by the members of the UN Security Council on February 24 has largely failed to hold.

Residents of Eastern Ghouta, which lies to the east of Damascus and was known as the breadbasket of the capital, have previously voiced their scepticism of a Russian-proposed "five-hour daily humanitarian pause" that began last Tuesday.

These pauses would supposedly create "humanitarian corridors" to allow the evacuation of those seeking medical treatment and the entry of aid convoys, but air strikes have continued to target civilians and residential areas.

Earlier, state government media, SANA, accused "terrorist groups" of stopping civilians from evacuating Eastern Ghouta through Wafideen for the seventh day in a row.

"The terrorist groups in Ghouta are still preventing civilians from leaving, even with ambulances and transport buses waiting on the other side of the safe corridors," SANA said.

Ground offensive

Meanwhile, the SOHR says, Syrian troops and pro-government allies have advanced further into Eastern Ghouta.

"Regime forces now control 33 percent, or a third, of besieged Eastern Ghouta," the group said on Monday.

Rami Abdel Rahman, SOHR's director, said the speed with which government forces are moving into the rebel-held enclave is because of the fact that these "operations so far are mostly conducted in farmland".

The Syrian government said it has recaptured control of 36 percent of Eastern Ghouta.

The country's Central Military Media said that troops are continuing their advance from the east and are only 3km from meeting troops advancing from the west, laying the ground for the dividing Eastern Ghouta into two parts.

Yet local journalists in the area said the territories captured were less than one quarter.

"Battles between the rebels and the pro-government troops are still being fought in a hit and run manner," one journalist in Douma told Al Jazeera, adding control of some of the territories was quickly changing.

In a press conference on Sunday, Syrian President Bashar al-Assad said that the Syrian army is attacking Eastern Ghouta "to restore stability and defend the people who are confronting terrorists".

"We will continue fighting terrorism ... and the Ghouta operation is a continuation of fighting terrorism," Assad said.

Jaish al-Islam, one of the armed opposition groups in Eastern Ghouta, said the government's "scorched earth policy" had forced rebels to retreat and regroup, but vowed to recover lost territory.

The group's spokesperson Hamza Bairakdar said that Jaish al-Islam had already begun offensive and that "hundreds of soldiers from the Syrian Army" have been killed in the last two weeks.