Israeli tanks forged into the southern Gaza Strip on Tuesday, drawing mortar fire from Palestinian militants and intensifying violence that has chipped away at a tenuous cease-fire.

Israel and Hamas have been trading fire for two weeks after nearly five months of relative quiet. The June 19 truce is due to expire next month, and both sides might be trying to dictate more favorable terms in anticipation of the agreement's renewal.

The Israeli military described the activity as "a routine operation to uncover explosive devices near the border fence in the southern Gaza Strip." It said two mortars were fired at troops, causing no injuries or damage.

Militant groups said they fired both mortars and rockets.

The tanks, backed by a bulldozer and military jeep, rumbled about a quarter-mile into the tiny seaside strip, residents and Gaza security officials said. Residents said they leveled lands along the border east of the city of Rafah. It was the first ground action in a week.

The tanks did not respond to the Palestinian fire.

At least 17 militants have been killed since the truce began unraveling, and by the military's count, militants have fired more than 140 rockets and mortars at Israel.

In an effort to squelch the rocket fire, Israel has kept cargo crossings into Gaza clamped shut for the most part, drastically restricting vital supplies.

Both Israel and leaders of Gaza's ruling Islamic militant Hamas movement have said they hoped the Egyptian-brokered truce could be preserved. But a small, Hamas-allied group said they consider the truce to have broken down, and Israel has threatened to hit hard if the rocket fire persists.

On Tuesday, a spokesman for the Hamas-run Interior Ministry accused Israel of subverting the truce.

"We call on the Palestinian factions to meet to begin an immediate re-evaluation of the calm," spokesman Ihab al-Ghussein said.

Before the truce was reached, militants barraged Israel with near-daily rocket attacks, provoking sometimes harsh military retaliation that killed hundreds of Palestinians, including many civilians.

In recent weeks, several dozen foreign activists have defied the siege, reaching Gaza by boat to try to draw attention to the misery the blockade has caused Gaza's 1.4 million people.

On Tuesday, a local anti-blockade activist, Amjad Shawwa, said Israeli seamen boarded a Palestinian fishing boat and arrested one of Gaza's foreign supporters and five Palestinian fishermen. Shawwa identified the foreigner as Andrew Muncie of Scotland.

The Israeli military had no immediate comment.