US Secretary of State Condoleezza Rice is in the Lebanese capital, Beirut, for a surprise visit as part of her five-day trip to the Middle East.
Ms Rice wants to show support for the anti-Syrian Lebanese groups
Ms Rice said she wanted to express US support for Lebanon as "they try to recover fully their sovereignty" after last year's pull-out of Syrian troops.
She is expected to meet Lebanese Prime Minister Fuad Siniora, but not pro-Syrian President Emile Lahoud.
Ms Rice has already visited Egypt and Saudi Arabia as part of her tour.
She met Egyptian President Hosni Mubarak in Cairo and her Saudi counterpart in Riyadh, in the hope of encouraging them to pressure Palestinian militants Hamas to renounce violence and recognise Israel.
But differences emerged and Saudi Foreign Minister Prince Saud al-Faisal said his country would give financial aid to the Palestinian Authority, even after Hamas, which won elections last month, takes control.
"We do not want to link international aid to the Palestinian people with considerations other than their terrible humanitarian needs," Prince Saud told reporters.
The Egyptian government also said it was premature to cut off international aid even if Hamas is at the helm.
Speaking to reporters as she arrived in Beirut, Ms Rice said she was seeking to lend support to Mr Siniora's government, which is dominated by anti-Syrian politicians.
"The sole purpose of this trip is to express support for the Lebanese people and for the Lebanese government as they try to recover fully their sovereignty they continue their efforts to reform," she said.
Syria was forced to withdraw troops it had stationed in Lebanon for more than a decade in response to international pressure and street protests following the assassination of former Lebanese Prime Minister Rafik Hariri in February 2005.
A UN investigation into the killing implicated leading Syrian and pro-Syrian Lebanese officials, though Damascus has denied it was involved.
Ms Rice is also expected to meet Lebanese Foreign Minister Fawzi Salloukh and Maronite Patriarch Nasrallah Sfeir. She will speak on the telephone with parliamentary speaker Nabih Berri.
Pro-Syrian groups are expected to protest against Ms Rice's visit, her first visit to Lebanon since July.