* Experts see Israel mounting tunnel-hunting missions
* Areas with population of 100,000 warned to evacuate
* Egypt, Qatar, Turkey trying to mediate ceasefire
By Nidal al-Mughrabi and Dan Williams
GAZA/JERUSALEM, July 16 (Reuters) - Israel urged the evacuation on Wednesday of several Gaza Strip areas where more than 100,000 people live, threatening ground operations after briefly holding fire under an Egyptian truce proposal that failed to stop Palestinian rocket salvoes.
Authorised by Prime Minister Benjamin Netanyahu's security cabinet to escalate an eight-day-old offensive, the military said it had sent out evacuation warnings in northeastern Gaza.
"Failure to comply will endanger your lives and the lives of your family," said recorded phone messages received by residents of Shejaia and Zeitoun districts, which sprawl out toward the border with Israel and have more than 100,000 residents.
Israeli experts predicted overland raids to destroy command bunkers and tunnels that have allowed the outgunned Palestinians to withstand air and naval barrages on Gaza and keep rockets flying.
Israeli shelling attacks killed at least seven Palestinians earlier on Wednesday, according to Gaza health officials who said the death toll in the coastal enclave had risen to 202 and that most of the dead were civilians.
Israel said 26 rockets were fired at it from Gaza, including at commercial hub Tel Aviv. Some were shot down by the Iron Dome interceptor. Others struck without causing casualties, emergency services said.
World powers urged calm, worried about spiralling casualties should Israel send tens of thousands of troops it has mobilised into Gaza. It is one of the world's mostly densely populated areas, its poverty exacerbated by the collapse of public works and displacement of at least 18,000 Palestinians who the UN said have taken shelter at its Gaza City schools.
On Tuesday, Israel unilaterally accepted an Egyptian blueprint for a ceasefire. The dominant Palestinian Islamist group Hamas, however, said it had not been consulted by Cairo and kept up rocket attacks while Israel held back for six hours.
With Palestinian fire having inflicted the first Israeli fatality of the conflict - a civilian bringing food to soldiers near Gaza - Netanyahu vowed to "expand and intensify" to stop persistent rocket strikes that have made a race for shelters a daily routine for hundreds of thousands in the Jewish state.
"The direction now is to continue air strikes and, if need be, enter with ground forces in a tactical, measured manner," an Israeli official said after the security cabinet met overnight.
The Israelis blew up a cross-border tunnel last week which, they say, may have been just one of many that Hamas has dug for deadly infiltration raids on their southern towns.
While tunnel-hunting incursions would be far short of a full-scale invasion and reoccupation, there is still the danger for Israel that risky and time-consuming missions could fall to Palestinian ambushes.
Hamas leaders have talked up their "tunnel campaign" against the Israeli enemy. One publicity video showed Palestinian fighters hauling rockets through a narrow passage to load onto a launcher that appears buried in an orchard. It is then fired remotely after its mechanised cover slides open.
Media reports on the Israeli military suggest it has just one dedicated tunnel-hunting unit, codenamed "Ferrets" - potentially no more than a few dozen commandos equipped with breathing apparatus, attack dogs and scouting robots.
Detecting the underground network is a problem for Israel - as shown by the continued rocket salvoes from Gaza despite its intensive, intelligence-guided air strikes on suspected sites.
Geologist Yossi Langotsky, a retired army colonel and Defence Ministry adviser, said on Army Radio that Israel had failed to develop technologies to "hear" hidden digs, allowing completion of the secret passages that now await activation.
Amos Yadlin, a former commander of Israeli military intelligence, said a crackdown on the tunnels was pressing, calling them "the second-most serious threat after the long-range rockets - or the primary threat, according to some".
Yadlin, who now heads the INSS think-tank at Tel Aviv University, played down the operational risk to Israel.
"The tunnels cannot be tackled except from the Palestinian side, but they are in relatively uninhabited areas," he said. "We would not have a problem maintaining control. I don't accept the argument that this would be a sinkhole back into Gaza."
Hamas has faced a cash crisis and Gaza's economic hardship has deepened as a result of Egypt's destruction of cross-border smuggling tunnels. Cairo accuses Hamas of assisting anti-government Islamist militants in Egypt's Sinai peninsula, an accusation that the Palestinian group denies.
The current hostilities were sparked by the kidnap and killing last month of three Jewish seminary students in the Israeli-occupied West Bank and the revenge murder of a Palestinian youth.
Hamas leaders have said any Gaza ceasefire must include an end to Israel's blockade of the territory, recommitment to a truce reached in an eight-day war there in 2012 and the release of hundreds of its activists arrested in the West Bank while Israel searched for the three missing teenagers.
Hamas also wants Egypt to ease curbs at its Rafah crossing with Gaza, imposed after the toppling of Islamist President Mohamed Mursi in Cairo last year.
(Additional reporting by Maayan Lubell and Allyn Fisher-Ilan in Jerusalem, Noah Browning in Gaza and Michael Georgy and Yasmine Saleh in Cairo; Writing by Dan Williams; Editing by Jeffrey Heller)