(Reuters) - The U.S. military launched airstrikes on Friday in Iraq and Syria against more than 85 targets linked to Iran's Revolutionary Guard (IRGC) and the militias it backs, in retaliation for last weekend's attack in Jordan that killed three U.S. troops.

The strikes, which included the use of long-range B-1 bombers flown from the United States, were the first in a multi-tiered response by President Joe Biden's administration to the attack by Iran-backed militants, and more U.S. military operations were expected in the coming days.

While the strikes did not target sites inside Iran, they signaled a further escalation of conflict in the Middle East from Israel's nearly four-month-old war with Palestinian Hamas militants in Gaza.

The strikes hit targets including command and control centers, rockets, missiles and drone storage facilities, as well as logistics and munition supply chain facilities, the U.S. military said in a statement.

U.S forces hit more than 85 targets spanning seven locations, four in Syria and three in Iraq, said the military.

The strikes targeted the Quds Force - the foreign espionage and paramilitary arm of the IRGC that heavily influences its allied militia across the Middle East, from Lebanon to Iraq and Yemen to Syria.

U.S. Lieutenant General Douglas Sims, the director of the Joint Staff, said the attacks appeared to be successful, triggering large secondary explosions as the bombs hit militant weaponry, though it was not clear if any militants were killed.

The Syrian Defense Ministry said that U.S. forces' "blatant air aggression" led to a number of civilians and soldiers being killed and others being wounded and some significant damage to public and private property.

"Occupying parts of Syrian lands by American forces cannot continue ... the Syrian army affirms continuing its war against terrorism until it is eliminated and is determined to liberate the entire Syrian territories from terrorism and occupation," the ministry said in a statement on Saturday.

The Pentagon's Sims said the strikes were undertaken knowing that there would likely be casualties among those in the facilities. He added that the weather was a key factor in the timing of the operation.

The Iraqi military said the strikes were in the Iraqi border area and warned they could ignite instability in the region.

"These airstrikes constitute a violation of Iraqi sovereignty, undermine the efforts of the Iraqi government, and pose a threat that could lead Iraq and the region into dire consequences," Iraqi military spokesman Yahya Rasool said in a statement.

There was no public response yet from Iran. Iranian state television, in its report on the strikes, described the Americans as terrorist forces.