Rescuers in Turkey have pulled more people from the rubble of Monday's earthquakes, but hopes were fading in Turkey and Syria that many more survivors would be found.
UN relief chief Martin Griffiths has said he expects the death toll to at least double, after he arrived in southern Turkey on Saturday to assess the quake's damage.
With a death toll of at least 29,605 in Turkey, the disaster is already in the list of the top 10 deadliest earthquakes ever. More than 3,500 have died in Syria, where death tolls have not been updated since Friday.
Between Monday and Saturday, the area experienced more than 2,000 aftershocks, according to Turkey's AFAD disaster authority.
Aid delivery to Syria hampered by divide between government, rebels
Syria's twelve-year civil war has impacted the delivery of aid to areas affected by the devastating quake.
The Islamist hardline group which runs the rebel-held northwest would not allow aid shipments from government-held parts of Syria, an unnamed source from the group told the Reuters news agency on Sunday.
"We won't allow the regime to take advantage of the situation to show they are helping," said the source from Hayat Tahrir al-Sham (HTS), which governs the opposition-held areas of the Idlib province.
Both the UN and the US classify HTS as a terrorist group. The group was formerly known as Jabhat al-Nusra, and served as a local affiliate to al-Qaida.
Northwestern rebels also turned back an aid convoy from Syria's Kurdish-led northeastern region on Thursday.
Meanwhile, the UN is trying to open two additional border crossings between Turkey and opposition-held Syria to facilitate aid deliveries, as HTS maintains it will only receive aid from Turkey.
Currently, Bab al-Hawa crossing is the only UN-recognized link between Turkey and the opposition-held areas. The roads around the crossing have been badly damaged by the quake.
Meanwhile in government-held areas, Syrian President Bashar al-Assad thanked the United Arab Emirates for being among the first countries to support Syria in the aftermath of the earthquake.
Emirati Foreign Minister Sheikh Abdullah bin Zayed Al-Nahyan visited Syria on Sunday, after his country pledged some $13.6 million (€12.7 million) to the country after the disaster. They then announced a further $50 million (€46.7 million) million in assistance.
UN admits aid failure in Syria's opposition-held areas
United Nations Under-Secretary-General for Humanitarian Affairs Martin Griffiths, visiting the Turkish-Syrian border, said Syrians had been left "looking for international help that hasn't arrived.''
He was referring specifically to areas in Syria's opposition-held northwest.
"They rightly feel abandoned," Griffiths wrote on Twitter, adding that he was focused on addressing that swiftly.
"My duty and our obligation is to correct this failure as fast as we can. That's my focus now," he added during the visit, where only a single border crossing is open for UN aid supplies.
The head of the Syrian "White Helmets" emergency response group accused the UN on Friday of failing to deliver appropriate humanitarian aid to opposition-held areas.
Turkey arrests building contractors after quakes
Turkish officials ordered the detention of 113 suspects allegedly involved in constructing some of the buildings that collapsed during the earthquakes.
Vice President Fuat Oktay said overnight that 131 suspects had been identified, and "detention orders have been issued for 113 of them."
Environment Minister Murat Kurum said at least 24,921 buildings across the region had collapsed or were heavily damaged.
Turkey's construction codes meet current earthquake-engineering standards but is not always enforced.
Authorities at Istanbul Airport on Sunday detained two contractors held responsible for the destruction of several buildings in Adiyaman, Turkish media reported. The pair were reportedly on their way to Georgia.
The state-run Anadolu Agency said that two more people were arrested in the province of Gaziantep suspected of having cut down columns to make extra room in a building that collapsed.
The detentions could help direct public anger toward builders and contractors, deflecting attention away from local and state officials who allowed sub-standard constructions.
Greek foreign minister visits quake disaster zone in Turkey
Greece's foreign minister, Nikos Dendias, is visiting quake-hit areas neighboring Turkey in a show of support.
He was met at the airport by his Turkish counterpart, Mevlut Cavusoglu before they flew to Antakya, where Greek rescuers are helping with search and rescue operations.
Despite a history of rivalry with Turkey, Greece was among the first European countries to send rescue workers and humanitarian aid a few hours after the disaster.
The Greek government has sent 80 tonnes of medical and first aid equipment.
According to the foreign ministry, Dendias and Cavusoglu will discuss ways Greece can further assist Turkey.
German rescue worker warns of disease
A German expert and relief worker has warned that the danger of disease is growing in quake-struck areas.
"In regions where people have no access to clean drinking water, there is a risk of epidemics at some point," said Thomas Geiner, a doctor with earthquake experience who is part of a rescue team from Germany's NAVIS aid organization.
Bodies trapped under rubble could contaminate the water supply, he warned. The lack of toilets was also a concern.
A Turkish rescuer, who did not provide her full name, described the situation in Antakya as desperate.
"The bodies are all over the roads, with only blankets on them," she said.
People in the town were wearing masks to cover the smell of death.
Germany to offer fast-track visa option for Turkish quake victims
Germany's Foreign and Interior ministries have announced plans to enable Turkish quake survivors who have relatives in Germany to temporarily stay with them.
The two ministries have set up a task force to fast-track the paperwork and reduce the necessary bureaucracy.
"The goal is to make the visa process for these cases as unbureaucratic as possible," said Foreign Minister Annalena Baerbock.
Interior Minister Nancy Faeser said this would be done with regular visas, which would be swiftly issued and remain valid for three months.
"We want to make it possible for Turkish or Syrian families in Germany to bring close relatives from the disaster region to join them without red tape," Faeser wrote on Twitter.
Germany is home to the largest Turkish community outside of Turkey.
'Absolutely unfair' to be accused of neglecting aid — EU envoy to Syria
The European Union's envoy to Syria has urged Damascus not to politicize issues of humanitarian aid, rejecting accusations that the bloc had failed to provide sufficient help to Syrians.
"It is absolutely unfair to be accused of not providing aid, when actually we have constantly been doing exactly that for over a decade and we are doing so much more even during the earthquake crisis," Dan Stoenescu told the Reuters news agency.
He said the EU had gathered more than €50 million ($53 million) to provide aid and back rescue missions and first aid in both government-held and rebel-controlled parts of Syria.
A 30-ton shipment of humanitarian aid from the Italian government — including four ambulances and 13 pallets of medical equipment — landed in Beirut on Saturday en route to Damascus.
The first shipment of earthquake-related aid crossed from Turkey into Syria's rebel-held enclave on Friday.
Humanitarian access to northern Syria is complicated by the civil war, while sending funds can be blocked or slowed by sanctions, despite an exemption for relief efforts.