The Pentagon said the first targets included two tanks, construction and military vehicles and a rocket launcher.
US air strikes are easing the passage of Libyan forces as they seek to clear Islamic State from the militant group's former North African stronghold of Sirte, a senior field commander said on Wednesday.
Mohamed Darat said the first strikes, which took place on Monday, had helped Libyan brigades under his command secure the Dollar residential neighbourhood by targeting militants who had been holding out on the district's edge.
Libya's U.N.-backed government requested the strikes nearly three months into a campaign that had slowed due to heavy casualties from sniper fire, mines and mortars.
"In the last two houses in this area we faced strong resistance so we asked (the U.S.) to hit that site," said Darat, speaking from a part of Dollar captured last week. "We moved back and they struck."
A U.S. defence official said there were five strikes on Monday and two on Tuesday. The Pentagon said the first targets included two tanks, construction and military vehicles and a rocket launcher.
The strikes were carried out by armed drones from Jordan and Marine Corps AV-8B Harriers from the USS Wasp, an assault ship located in the Mediterranean Sea, the U.S. official said, adding that intelligence-gathering drone flights were being operated from Sigonella air base in Sicily.
Losing Sirte would be a huge blow for Islamic State, which took control of the city midway along Libya's Mediterranean coastline last year. The group is already under pressure from U.S.-backed campaigns in Syria and Iraq.
Libyan commanders say a few hundred Islamic State fighters are now encircled in the centre of Sirte, though they have retained control of four neighbourhoods.
The advance through residential areas would be gradual, Darat said. "We'll do what we did in Dollar and move forward house by house.
"We're resting now and if there are air strikes it will make our lives easier, but we will advance with or without them."
The forces fighting in Sirte are mainly composed of brigades from the nearby city of Misrata, which counter-attacked in early May when Islamic State advanced up the coast west of Sirte.
Many of them are volunteers and former rebels who fought in the uprising that toppled Muammar Gaddafi five years ago. At least 350 brigade members have been killed and more than 1,500 wounded since May.
Almost all of Sirte's 80,000 residents have fled the city, and the streets are mainly deserted. Each day of heavy fighting tends to be followed by a lull of several days.
On Wednesday brigade fighters rested in buildings or in the shade of trees, eating green almonds and cooling off with iced drinks, the quiet broken by occasional crackle of gunfire.
They welcome the air strikes, some saying they should have come sooner.
"We wish they'd do it on a more regular basis," said Mohamed Abu Dabbous, a fighter on the front line between the Zafaran and Area Two districts.
He said that when it tries to move forward his unit is exposed to fire from a cluster of about 20 unfinished apartment blocks used by Islamic State snipers, buildings he said would make an obvious target for U.S. strikes. His fighters also risk being hit by mines.
"In 2011 we dealt with Gaddafi's snipers, but it was easier then because there weren't any landmines."