BASRA, Iraq — Five days into the Iran-Israel ceasefire, the first international mine-action teams fanned out across southern Iraq, southern Lebanon and Iran’s western border provinces on Monday to begin the painstaking work of clearing missile debris, cluster submunitions and damaged ordnance from neighborhoods, fields and roadsides that families are increasingly determined to reach.

The United Nations Mine Action Service said in a situation report Monday morning that 19 teams from six contributing organizations had been deployed across the four affected countries, with another 27 expected by the end of the week. The contamination, agency officials cautioned, was unusually heterogeneous: missile fragments from intercepted Iranian barrages, unexploded warheads from strikes that failed to detonate on impact, abandoned munitions at hastily evacuated launch sites and, in at least three confirmed locations in southern Lebanon and western Anbar, cluster submunitions whose origin remained under investigation.

“This is not a single battlefield. This is dozens of small ones spread across an area larger than France, and the threats are not the same in any two of them,” said Pehr Lodhammar, the UNMAS senior program manager who has been coordinating the regional response from Amman. “Until we know what is on the ground in each location, we cannot tell a family it is safe to go back to their kitchen, let alone their wheat field.”

The most immediate concern, mine-action officials said, was the slow-moving return of displaced families ahead of clearance work. UNHCR has registered roughly 14,800 returns since Friday, the bulk into Khuzestan province and southern Iraq, and Iraqi army units along the border have begun escorting bus convoys back to villages east of Basra. In several documented cases over the weekend, returnees encountered debris in courtyards, on rooftops and along irrigation canals before any survey had been conducted, prompting Iraq’s Directorate of Mine Action to issue a public bulletin Sunday urging residents not to handle metal fragments larger than a fist.

Two children were killed Saturday afternoon in the village of Al-Hartha, north of Basra, when one of them picked up what authorities later identified as a partially detonated submunition that had been lying in a date palm grove. A third child was hospitalized in critical condition. The incident, the first confirmed fatal civilian casualty of unexploded ordnance since the ceasefire took effect, was cited Monday by aid agencies as the reason a more aggressive public-awareness campaign was being rushed into print, radio and social media across the affected region.

“We knew this would happen and we still were not fast enough,” said Yusra Kadhim, the Iraqi coordinator for the Mines Advisory Group, in an interview at the organization’s Basra field office. “Children pick up anything shiny. Adults try to move debris off their land because they want to plant. Everyone wants to get back to normal. The problem is that the things in their yards are not yet normal.”

Lebanon presented a separate set of difficulties. Israeli strikes during the war’s middle weeks hit suspected Hezbollah weapons depots and rocket-launch sites in the Bekaa Valley and the southern suburbs of Beirut, and final-week strikes targeted positions along the Litani River. The Lebanese Mine Action Center said its teams had identified 47 sites requiring survey across the south, including residential blocks in Nabatiyeh and the towns of Bint Jbeil and Khiam, where some unexploded munitions remained lodged in upper-story walls.

“We have done this before, in 2006 and after, and we know what works,” said Brigadier General Ziad Nasr, who heads the center, in remarks to Lebanese state media. “What is different this time is that the speed of return is higher, the funding picture is less clear, and the technical mix of contamination is broader. We need international partners on the ground inside two weeks, not two months.”

The contamination problem in Iran has been harder to characterize from outside the country. Iranian authorities have not invited international mine-action organizations to operate inside Iranian territory, though the Iranian Red Crescent Society said Monday that its own teams, trained in past years on legacy ordnance from the Iran-Iraq war, had begun surveys in Khuzestan, Bushehr and parts of Isfahan province. Iranian state television showed footage Sunday evening of a clearance team destroying what officials identified as a damaged Israeli air-to-ground munition in a field outside Ahvaz.

International coordination on the Iranian side is expected to run through Tehran’s relationship with the U.N. and through bilateral channels with Pakistan and Turkey, both of which have offered technical support, according to a senior U.N. official in Geneva who spoke on condition of anonymity because he was not authorized to discuss diplomatic communications. The official said donors had so far pledged roughly $34 million toward a $190 million regional mine-action appeal that the U.N. expects to formalize at the Marseille conference next week.

The submunition question has acquired particular political weight. Cluster munitions are banned under the 2008 Convention on Cluster Munitions, which neither Israel nor Iran has signed, and the documentation of submunitions in three locations — two in southern Lebanon, one in western Anbar — has prompted advocacy groups to call for investigations into who used them and when. Human Rights Watch said in a statement Monday that it was sending a research team to the region. The Israeli Defense Forces declined to comment on specific munitions, and Iranian state media did not address the question.

“Attribution will matter for the legal record, but for the family in front of the date palm grove, attribution is not the urgent thing,” said Soraya Boukhari, a Geneva-based humanitarian disarmament researcher. “The urgent thing is whether someone with the right equipment and the right training is going to be standing in that grove tomorrow morning. That is what the next four weeks are about.”

Aid agencies said the practical bottleneck would be experienced personnel. The global pool of qualified explosive-ordnance disposal technicians is small, and several organizations have been simultaneously drawing on it for parallel operations in Ukraine, Sudan and Gaza. Recruitment cycles for new clearance teams typically run six to nine months, an interval mine-action officials said was not compatible with the speed at which families were trying to return home.

UNMAS said priority survey work in Iraq would focus this week on residential and agricultural areas within 40 kilometers of the Iranian border, and that mobile risk-education teams using mosque public-address systems, school assemblies and provincial radio would be operating in 11 affected provinces by Wednesday. Officials said additional teams and a revised funding appeal would be announced after a coordination meeting in Geneva later in the week.