China’s navy test-launched a long-range ballistic missile Monday from a nuclear-powered submarine — a move that experts said showed Beijing’s increasing skill and capability as part of its nuclear deterrence strategy.

The move also drew protests from the U.S. as well as countries in Asia and the Pacific. It was the second time China had fired a ballistic missile into international waters in recent years. While it gave some countries in the region prior notice, some said it was not enough notice, and experts say the launch exacerbates tensions around increasing militarization in Asia.

Here’s what we know, and what we don’t, about the missile launch.

Experts think it could be a JL-2 or a JL-3 ballistic missile

China announced the missile test publicly on Monday only after the launch, saying that it was fired into the Pacific Ocean. In a brief statement, the official Xinhua News Agency said the launch was part of routine annual training, complied with international law and practice, and was not directed against any country or target. It didn’t provide details about the type of missile.

The missile was carrying a dummy warhead, not a nuclear one. The act of launching in international waters was rare, although the U.S. has also done so with its own missile testing.

Xinhua published a photo of the missile on Tuesday without additional details. Experts say it could be either a JL-2 or a JL-3, both submarine-launched ballistic missiles, though most said the available imagery was not clear enough to tell.

The state-owned tabloid Global Times said it was “most likely” a JL-3 missile with a range exceeding 10,000 kilometers (6,200 miles). The JL-2 has a shorter range.

The New Zealand government said the missile was launched into treaty waters in the South Pacific Nuclear Free Zone, violating the intention of the agreement.

The zone was established by the 1986 Treaty of Rarotonga, which prohibits nuclear weapons throughout the region. China ratified the protocols in 1987, pledging not to test nuclear weapons within the zone or threaten to use them against signatories with territory in the region.

Australia, Japan, and other countries protest

While China has told other countries to “avoid overinterpretation” in response to the criticism, experts say the concerns from other countries have some basis.

Much of the concern is a result of lack of clear information, said Drew Thompson, a senior fellow at the S. Rajaratnam School of International Studies in Singapore. “China’s military modernization and buildup have occurred without concurrent increases in openness and transparency, resulting in uncertainty about China’s intentions.”

Australian Prime Minister Anthony Albanese said that China did not provide enough notice to the government.

“There is no doubt that this is a provocative act by China which does destabilize the region,” he told reporters Tuesday while in Honiara, in the Solomon Islands.

“This was a test of a nuclear-capable intercontinental ballistic missile fired from a nuclear-powered submarine. That is of real concern because what we need is less nuclear weapons, certainly not more. And the fact that this test took place yesterday with very little notice is of real concern,” Albanese added.

New Zealand had said the same Monday, with Foreign Minister Winston Peters calling it “unwelcome and concerning.”

Solomon Islands Prime Minister Matthew Wale, also speaking to reporters in Honiara Tuesday, said that “China is a good friend of Solomon Islands, but this is not something a friend does. This is not … good in our region.”

Read More: What to know about China’s rare ballistic missile test and why it raises concerns