TEL AVIV, Israel — As the cease-fire between Israel and Hezbollah looked increasingly fragile yesterday, Israel’s foreign minister warned that the situation between the warring sides in southern Lebanon was “explosive.”

“Time is working against those who would like to see this resolution applied,” Tzipi Livni said after meeting with her French counterpart in Paris. “We are now in the most sensitive and explosive position.”

Yesterday, an Israeli soldier died after entering a minefield and three Lebanese soldiers were killed trying to defuse a cluster bomb, according to wire reports. And Israeli officials have confirmed that, notwithstanding the cease-fire, the Israel Defense Force considers senior Hezbollah commanders legitimate targets.

Over the weekend, the Israeli military bombed positions in the Bekaa Valley, saying it was preventing the resupply of Hezbollah. Israel appears to be in a precarious position. Although many of its soldiers are leaving southern Lebanon, Prime Minister Olmert has pledged more operations to stem the tide of weapons to Hezbollah until the 15,000-troop force called for in U.N. Security Council resolution 1701 fills the security vacuum.

That force has yet to materialize, however. The French have reneged on promises to send substantial numbers of troops to southern Lebanon. And while Italy has pledged up to 3,000 soldiers for the force, other donors include countries like Malaysia and Indonesia, where the faith of choice for some is the same Islamism followed by the Hezbollah fighters they are supposed to disarm.

Two other countries weighing whether to send troops to Lebanon are Russia and Turkey, countries that Israeli officials have said played a role in supplying Hezbollah. One Likud member of the Knesset’s foreign affairs and defense committee, Yuval Steinitz, said Tuesday that Israel’s presence in southern Lebanon could last for a few months.

“Hezbollah will rebuild and we will be under pressure to leave. It is not good to leave the IDF there for too long. We will stay a few months, then we pull out without the agreement and it will be a big mess. We did not use the opportunity to eliminate Hezbollah’s military presence. We did not complete the job and we are going to pay the price,” he said.

Pressure is already mounting on Israel to lift its air and sea blockade of Lebanon. Prime minister Siniora of Lebanon called on America yesterday to pressure Israel to “lift the siege.”

Before his meeting with Ms. Livni yesterday, the French foreign minister, Philippe Douste-Blazy, told French Channel 2 television, “If Lebanon is going to be reconstructed, if Lebanon is going to take off economically, the blockade must be lifted.”

But as international leaders pushed Israel to open Lebanon’s ports and airspace, Syria threatened yesterday to shut down its border with Lebanon if an international force was deployed there. After meeting his Syrian counterpart in Damascus, Finland’s foreign minister, Erkki Tuomioja, said, “They indeed do not want this and they announced they will close their borders if this takes place,” according to Reuters.

The Syrian threat comes as a surprise, as one of the chief Israeli grievances the U.N. cease-fire addresses is Syria’s role in allowing arms to flow to Hezbollah from Iran. One of Israel’s aims for the international force is to secure those borders to cut down on the arms smuggling.

However, if Syria closes the border entirely, then Lebanon will be entirely cut off from the Arabian Peninsula, as it now has no diplomatic relations with Israel. One possibly positive piece of news for Israel yesterday was Mr. Douste-Blazy’s hint that France may consider sending more troops to southern Lebanon pending the outcome of a meeting Friday of European Union foreign ministers in Brussels.