Iran shot down the drone after weeks of festering tension amidst a spate of attacks on oil tankers in the Gulf region.
The current crisis comes at a tumultuous moment at the Pentagon, where the acting secretary of defense, Patrick Shanahan, is stepping down this weekend.
"On the other hand, let's remember this regime in Iran is responsible for killing hundreds of American soldiers in Iraq when they were designing an (improvised explosive device) ... for the exclusive objective of penetrating American armored vehicles and killing the American soldiers inside", Toomey said shortly after an unrelated news conference at UPMC Children's Hospital of Pittsburgh in the city's Lawrenceville neighborhood.
Keane described the administration's maximum pressure campaign was "first rate".
A Pentagon spokeswoman, Commander Rebecca Rebarich, said on Saturday: "We stand by where we said the aircraft was operating in global airspace". "That has got to be our strategic focus", he told Fox News host Leland Vittert.
Trump's assertion that he learned only at the last minute of his military advisers' casualty estimate does not align with the usual way a president is briefed on military attack options.
Tensions between Iran and the United States almost escalated into a unsafe direct confrontation on Thursday as President Donald Trump approved airstrikes against Tehran following the Islamic Revolutionary Guard Corps' downing of a USA spy drone, but abruptly backtracked on his decision. "How many people would be killed, in this case Iranians?"
Trump's decision prompted Rep. Justin Amash, R-Mich., and House Speaker Nancy Pelosi, D-Calif., to demand he seek approval from Congress before approving more strikes. The president now, because he's exercised restraint, has leverage. "Yeah, I do." Trump said.
"We do not need to go to war with Iran over an unmanned drone until we have more information".
"We are putting additional sanctions on Iran", Mr Trump told reporters.
A British Foreign Office official will visit Iran and call for "urgent de-escalation in the region and raise United Kingdom and worldwide concerns about Iran's regional conduct" during talks with Tehran's government.
"The downing of the USA drone had an explicit, decisive and clear message that defenders of the Islamic Iran's borders will show decisive and knockout reactions to aggression against this territory by any alien", he said.
Iran has threatened to breach the deal if the European signatories to the agreement fail to salvage it by shielding Tehran from U.S. sanctions.
"We will brief the council on the latest developments with regard to Iran and present further information from our investigation into the recent tanker incidents", Reuters news agency quoted the U.S. mission to the United Nations as saying in a note to council colleagues.
While the United States has dispatched a carrier battle group and a bomber strike group led by nuclear-capable B-52s, as well as another 2,500 U.S. troops, joining the 20,000 already deployed in the region, it is still not prepared for such a war.