WASHINGTON, Feb 2 (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 U.S., are 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 are expected in the coming days.

While the U.S. strikes did not target sites inside Iran, they signal a further escalation of the conflict in the Middle East from Israel's more than three-month-old war with Palestinian Hamas militants in Gaza.

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

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.

But Sims added that the strikes were taken 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.

Syrian state media said on Friday that an "American aggression" on sites in its desert areas and at the Syrian-Iraqi border resulted in a number of casualties and injuries.

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.