US Secretary of State Condoleezza Rice (R) is accompanied by Lebanese Prime Minister Fuad Siniora (L). Rice is in Beirut at the start of a high-stakes mission to try to end the devastating conflict in Lebanon, even as Israeli troops were locked in deadly combat with Hezbollah guerrillas. -Xinhua/Reuters

US Secretary of State Condoleezza Rice paid a surprise visit to Lebanon on Monday in a diplomatic move to push for a "sustainable" peace, well-informed sources said.

The top US diplomat, on her first visit to Mideast since violence between Israel and Lebanon's Hezbollah erupted on July 12, held separate meetings with Lebanese Prime Minister Fouad Siniora and Parliament Speaker Nabih Berri in the Lebanese capital Beirut.

During the meetings, Rice insisted that Washington would only work toward a "sustainable" truce although a ceasefire was urgent, said the sources.

She also said that Hezbollah must release two Israeli soldier sit took hostage and pull back from the border with Israel before any ceasefire, the sources added.

Rice also told the media that she was "deeply concerned" about the Lebanese people's sufferings and the humanitarian situation. Siniora, on his part, told Rice that 750,000 people in Lebanon had been displaced due to the Israeli assault and that the country had suffered multi-billion U.S. dollar losses, according to a statement issued by his office.

The United States has so far justified Israeli attacks on Lebanon, refusing to push for an immediate ceasefire which it said would only lead back to the status quo.

The Lebanese side has repeatedly called for a ceasefire as soon as possible, warning of a possible humanitarian disaster. After the brief visit to Lebanon, Rice started her visit to Israel, during which she is planned to meet Israeli Prime Minister Ehud Olmert.

She will also hold talks with Palestinian President Mahmoud Abbas before heading to Rome for a multi-party meeting over the situation in the Middle East region on Wednesday.

Israel has kept up a 13-day-old onslaught against the Lebanese Shiite group Hezbollah since Hezbollah guerillas captured two Israeli soldiers and killed eight others during cross-border attacks on July 12.

Meanwhile, the Israeli army continued a massive air and ground offensive in the Gaza Strip launched almost a month ago aimed to free another Israeli soldier kidnapped by Palestinian militants and halt Palestinian rocket attacks.