"We face many obstacles", said Sutopo Nugroho, spokesperson for the Indonesian Disaster and Mitigation Agency, at a media briefing Monday.
He said the communities of Sigi and Balaroa have not been counted yet, meaning the toll is likely to rise.
According to authorities, aid has been slow to trickle in, delayed by severe damage to Mutiara Sis Al Jufri Airport in Palu, which was closed for 24 hours after the tsunami but has since reopened to limited flights.
For survivors, the situation is growing increasingly desperate as they wait for supplies and aid.
It is unclear whether the Britons, who will act as humanitarian advisers, will move around with support from the Indonesian military or the UK's Ministry of Defence.
Dozens of aid organisations (including several Christian entities) are trying to send humanitarian help to the island, but several cities and towns have been hard to reach.
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Nugroho said 114 foreigners were in Palu and nearby Donggala during the disaster. Many survivors were blocking trucks carrying aid to help themselves to the contents as they said they had gone hungry and thirsty for days. With supplies dwindling, administrator Kasman Lassa said citizens were taking food and other essential items from shops. Do not take chairs, or television. Photos were taken of the corpses before they were buried so they could be identified by relatives.
The confirmed death toll from an quake and tsunami on Indonesia's Sulawesi island has risen to 1,234, from 844, the national disaster mitigation agency said on Tuesday.
"The prison no longer had enough food", Utami said.
State news agency Antara reported that one bridge was damaged in Wula Waijelu, but there were no other immediate reports of damage.
Indonesia is a vast archipelago stretching a similar distance to that between NY and London. Indonesia is located on the Ring of Fire, an area of high seismic activity that borders the Pacific Ocean, meaning earthquakes are common and there's no telling when the next one will hit - just two months ago a major one hit near the city of Lombok, and killed hundreds.
Anadolu Agency via Getty Images Houses and vehicles damaged by natural disaster and tsunami are seen on Talise beach area, Palu, Central Sulawesi.
After a 7-point-5 magnitude quake struck the area on Friday, .it triggered tsunami waves as high as six meters.
Teams were searching for trapped survivors under destroyed homes and buildings, including a collapsed eight-storey hotel in the city, but they needed more heavy equipment to clear the rubble.