"The fact the US is sending military aid will probably not go well with the oposition," Zeina Khodr, Al Jazeera's Lebanon correspondent, said.
She said the oposition accuses the Lebanese government of "working for the interests of the US and implementing a US-plan for what they are calling a 'new Middle East'".
"From outside Lebanon it's very easy to condemn the Lebanese army and government for what they are doing against Fatah-al-Islam"
Rabih, Mansourieh El Metn, Lebanon
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The diplomat said the US would send eight airplanes carrying military equipment in total.
The Lebanese army has been fighting the Fatah al-Islam movement in the Palestinian refugee camp of Nahr al-Bared in north Lebanon.
"All the political parties [in Lebanon] are supporting the army," Elias Hanna, a retired Lebanese general, told Al Jazeera.
"The Palestinian Authority and the PLO are also denying Fatah al-Islam is [speaking for the] Palestinian [people] because it is a terrorist organistaion."
Sporadic gunfire exchanges punctured the lull in the fighting on Friday as the Lebanese army continued to build up around Nahr el-Bared, near the port city of Tripoli.
Speaking to Al Jazeera, a spokesman for the Fatah al-Islam group, said the group's fighters were committed to a truce with the Lebanese army.
The AFP news agency reported that death toll in the fighting had risen to 78.
Thousands of Palestinian refugees remain trapped inside.
On Thursday, Condoleezza Rice, the US secretary of state, gave her full backing to the Lebanese government.
"I certainly hope that the Lebanese government will be able to deal with these extremists," Rice said.
"It's just another example of extremists in the Middle East who are trying to destabilize democratic governments."
The Lebanese An Nahar newspaper said that a first US airplane had arrived late on Thursday from Kuwait, with two from Egypt on Friday.
Late on Thursday, a United Arab Emirates air force airplane also arrived with supplies.
The Lebanese military did not comment on the airlift, a sensitive issue in the country.
The remainder will be coming from other Arab states where the US maintains weapons depots, it said.
The United States provided $40m in military aid to Lebanon last year and already this year has supplied hardware worth $5m.