America's defense chief said Wednesday that an al-Qaida branch is making "great gains" on the ground amid the chaos in Yemen, and that the U.S. will have to rethink how it prevents the group from launching attacks in the West.

Defense Secretary Ash Carter, in Tokyo to work on deepening the U.S.-Japan alliance, said the collapse of the central government in Yemen makes it harder to conduct counterterrorism operations against the group called al-Qaida in the Arabian Peninsula.

"That doesn't mean that we don't continue to take steps to protect ourselves. We have to do it in a different way, but we do and we are," he said, without offering any specifics.

The group is known to have ambitions to strike Western targets, including the United States.

Carter said that as Shiite rebels advance in Yemen, the al-Qaida branch there is taking advantage of the disorder to seize territory. "You see them making great gains on the ground," he said.

He said the U.S. is providing intelligence, surveillance, reconnaissance and logistics information and "some resupply of equipment and munitions" to Saudi Arabia, which has launched airstrikes against the rebels in neighboring Yemen.

Carter, who travels to South Korea later this week, is on his first trip to Asia since becoming defense secretary in February.

Japan and the United States are nearing completion of the first revision in 17 years of the U.S.-Japan Defense Guidelines, an agreement that will "transform" the bilateral alliance, Carter said at a news conference after meeting with his Japanese counterpart in Tokyo.

The new guidelines, expected to be formally approved in about three weeks, "will help us respond flexibly to the full scope of challenges we face, both in the Asia-Pacific and around the globe," he said.

Japanese Defense Minister Gen Nakatani said he and Carter agreed that relocating a U.S. Marine base in Okinawa to another part of the southern Japanese island is the "only solution" to closing Futenma base, which lies in an urban area.

Many in Okinawa, including the current governor, oppose the construction of the replacement base in a less populated area, arguing that the facility should be moved off the island entirely.

The new defense guidelines are expected to lay out the framework for Japan to play a bigger role in regional security, as the government loosens constitutional restrictions on the use of its military.

They will also outline cooperation in new areas such as space and cyberspace. Nakatani said the two defense agencies have agreed to study the establishment of a new working group on space.