Dozens more killed in Gaza as Israel strengthens ground offensive

At least 34 people were killed in Gaza on Saturday as Israeli army bombardments intensified on the second day of a ground offensive it says is aimed at destorying Hamas' military wing.

Tank fire along eastern Gaza, bordering Israel, caused many civilian casualties, according to eyewitnesses on the ground, amid artillery attacks across the territory. Drones, jets and attack helicopters patrolled the skies. Al Jazeera correspondent Stefanie Dekker reported "relentless and constant thuds" of tank fire along the border, coming every 10 seconds.

The Gaza health ministry said the death toll over 12 days now stands at 333. That figure includes 77 children, 24 women and 18 senior citizens. More than 2,385 people have been injured and more than 50,000 displaced.

Five Israelis, three soldiers and two civilians have been killed since the start of the conflict. Two of the soldiers were killed Saturday in a cross-border clash with members of Hamas, the Israeli army said. Four other soldiers were wounded.

In another development Saturday, agencies said Egyptian soldiers in north Sinai prevented an aid convoy of activists from reaching the Rafah border crossing with the Gaza Strip.

An army officer at the Balloza checkpoint, one of many along the desert highway to Rafah, told an AFP correspondent that the security situation in the peninsula was too unstable to allow the convoy of 11 buses and 500 activists to pass.

There was a brief scuffle between some activists and soldiers but no arrests were made.

Egypt usually keeps the crossing closed, citing a counterinsurgency operation against fighters in north Sinai, but has allowed entry to Palestinians wounded in the conflict between Hamas and Israel.

The Egyptian military had earlier said it was sending 500 tons of food and medical aid to Gaza.

The intense shelling came hours after President Barack Obama said Washington was "deeply concerned about the risks of further escalation and the loss of more innocent life" and just days after Hamas hadrequested an enforceable cease-fire. Obama said he hopes Israel will operate "in a way that minimizes civilian casualties."

The ground offensive is a new phase in Israel's "Operation Protective Edge," which the military said would destroy tunnels used by Hamas. Israeli Prime Minister Benjamin Netanyahu has said the ground operation is necessary to deal with the tunnels but admitted there was "no guarantee of 100 percent success."

In addition to a mounting death toll, the offensive has prompted thousands of Palestinians to flee from their homes. The United Nation's relief agency said more than 50,000 have requested shelter. The international body is housing many in 44 schools across Gaza and said the number of refugees will likely rise as Israel’s ground operation intensifies.

The offensive failed to prevent an incursion by a tunnel into Israel by a Palestinian fighter on Friday. But his planned attack was foiled by the Israeli military, with one fighter killed in the skirmish.

The Palestinian and Israeli U.N. ambassadors traded blame for the violence, with Israel's Ron Prosor insisting no other country would "tolerate... terrorist" rocket fire at its citizens.

U.N. chief Ban Ki-moon arrived in the region on Saturday to bolster truce efforts.

Ban aims to help Israelis and Palestinians "in coordination with regional and international actors, end the violence and find a way forward," the under secretary-general for political affairs Jeffrey Feltman told the Security Council.

Al Jazeera and wire services