Nearly 20 Palestinians and an Israeli soldier were killed as troops clashed with militants in Gaza today after Israel launched a ground operation aimed at destroying tunnels and halting rocket fire by the enclave's Hamas rulers.

Israel intensified its 11-day campaign against Hamas by sending in tanks and troops late yesterday after becoming increasingly exasperated with unrelenting rocket fire from Gaza on its cities, especially following Hamas's rejection of an Egyptian ceasefire plan earlier in the week.

The Israeli military announced its first casualty since the start of the ground operation, saying one soldier was killed in the northern Gaza Strip.

The circumstances behind his death were not immediately clear, with Hamas's military wing saying it ambushed Israeli units in the northern town of Beit Lahiya and caused casualties but Israeli media saying it was likely a case of friendly fire.

Gaza health officials said 19 Palestinians have been killed since the ground operation began late yesterday. The military said it killed 14 militants in different exchanges of fire. It was not immediately clear if the militants were among those reported killed by Gaza authorities.

Israel's chief military spokesman, Brigadier General Moti Almoz, told Army Radio "there were a number of points of friction through the night" and said the military was investigating the circumstances behind the soldier's death.

In a statement, the military said it targeted rocket launchers, tunnels and more than 100 other targets. The military said "a number" of soldiers were injured throughout the night.

In Gaza City, plumes of black smoke could be seen rising from areas near the border with Israel and explosions echoed throughout the city.

Israeli aircraft have struck more than 2,000 targets in Gaza and 260 Palestinians have been killed since the start of the fighting.

The Israeli military said 50 rockets have been fired at Israel since the start of its ground operation, out of more than 1,500 since the fighting began last week. An Israeli civilian was killed earlier this week.

Israel said it launched an open-ended assault on several fronts, with the primary aim being to destroy underground tunnels into Israel built by Hamas that could be used to carry out attacks.

Earlier yesterday, 13 heavily armed Hamas militants had tried to sneak into Israel through such a tunnel, but were stopped by an air strike after they emerged some 820ft (250m) inside Israel.

Israeli officials have said the goal is to weaken Hamas militarily and have not addressed the possibility of driving the Islamic militants from power. However, Hamas has survived Israeli offensives in the past, including a major ground operation in January 2009 from which it emerged militarily weaker, but then recovered. Hamas has since assembled thousands of rockets and built a system of underground bunkers.

Israel had been reticent about launching a ground offensive for fear of endangering its own soldiers and drawing international condemnation over Palestinian civilian deaths.

But Israeli public opinion appears to strongly support the offensive after days of unrelenting rocket fire from Gaza and years of southern Israeli residents living under the threat.

Israel's Cabinet was set to meet later today to be briefed on the assault.

Uri Ariel, a Cabinet minister from the hard-line Jewish Home party, told Israel Radio that air strikes alone would not neutralise Hamas's weapons. He said he expected that ground forces would penetrate Gaza further.

"There won't be a choice. The military will need to enter deeper," he said.