Acting US Defence Secretary Patrick Shanahan warned any nations that might be considering anti-satellite (ASAT) weapons tests like the one India carried out on Wednesday to "not make a mess" in space, noting the debris that can be left behind.
"My message would be: we all live in space, let’s not make it a mess. Space should be a place where we can conduct business. Space is a place where people should have the freedom to operate," Shanahan told a small group of reporters on Wednesday, without saying whether he believed India's test left debris.
He said the United States was still studying the Indian test.
"You cannot make (space) unstable. We cannot create the debris problem that ASAT tests create. So, thoughtfulness goes a long way."
India's foreign ministry played down any risk of debris, noting the test was in low-earth orbit, and said the remnants would "decay and fall back on to the earth within weeks."
India would only be the fourth country to have used such an anti-satellite weapon after the United States, Russia and China, Prime Minister Narendra Modi said.
The United States ran the first anti-satellite test in 1959, when satellites themselves were rare and new.
Shanahan noted that, given the increasing global reliance on space, it was importance to create rules of the road for space.
"I think not having rules of engagement is worrisome. So, how people test and develop technologies is important," he said, adding: "I would expect anyone who tests does not put at risk anyone else's assets."