New US drones and a radar to defend against North Korean missiles will be deployed in Japan, senior politicians from both sides said Thursday as they met to rebalance their security alliance.

US Secretary of State John Kerry, Secretary of Defense Chuck Hagel, Japanese Foreign Minister Fumio Kishida and Defence Minister Itsunori Onodera held the first review of the cornerstone alliance in 16 years, after years of rising Chinese power and provocations from Pyongyang.

"Our goal is a more balanced and effective alliance, where our two militaries are full partners working side-by-side with each other, and with other regional partners, to enhance peace and security," Kerry said after the meeting.

Washington has long expressed frustration at Japan's narrow interpretation of its pacifist constitution, which precludes the right of first strike and confines military action to defence against a direct attack on Japanese people or property.

At the same time a resurgent centre-right, in the form of popular Prime Minister Shinzo Abe, is increasingly nervous about China's intentions in the region.

Abe has said he wants Japan's well-resourced and well-trained military to play a more active role -- chiefly the ability to come to the aid of its ally if it were attacked, for example by a North Korean missile attack on a US base.

However, some on Japan's left are uneasy at the idea of a more active military and the subject raises hackles in China, which accuses Tokyo of mulling a return to the militarism of World War II.

Fears over North Korea's missile and nuclear programme were high on the agenda, with the US pledging new hardware in Japan.

"Another key priority is missile defence, given the threat posed by North Korea's ballistic missiles to both of our countries," said Kerry

"Today we announced our plans to deploy a second TPY-2 radar to Kyoto Prefecture. This additional radar will bolster our ability to defend the US homeland and Japan against North Korean ballistic missiles, and enhances an important 21st century alliance capability."

Pyongyang conducted its third and most powerful atomic test in February, triggering months of heightened military tensions on the Korean peninsula.

A US think-tank said Wednesday after analysing new satellite imagery that it is clear that Pyongyang has restarted an ageing plutonium reactor.

The US also said it would be stationing drones in Japan, spreading out an asset that has become key to the US military machine. A US source said unmanned reconnaissance vehicles had been used in Japan before, but had never been stationed here.

Moving to Guam

The so-called "2+2" meeting also revisited a 2009 agreement intended to move 8,000 Marines off Okinawa, the southern island chain that hosts the majority of the 47,000 US troops in Japan.

Around half of the Marines will be moved to Guam by early next decade, with Japan meeting $3.1 billion of the $8.6 billion cost of this move.

As has become customary at US-Japan meetings over the last 12 months, the American side reiterated its position that the Senkakus, which Beijing calls the Diaoyus, fall under the two countries' security treatment as an area under Japanese control.

That means if the islands were invaded, the US would be forced to respond.

Japan is keen to extract this reassurance at every opportunity, as a way of bolstering its case against China and as a warning against Beijing overreaching.

Washington looks every time to strike a wary balance between promising to backstop its ally and giving too much succour to less moderate voices in Tokyo, who might push for a more provocative course against China.

"The United States has made it clear the longstanding policy that has not changed, that while we don't take positions on the sovereignty of the Senkaku islands, we do recognise Japan's administration of those islands," Kerry said.

"And we have urged the parties not to engage in any unilateral actions that challenges that and rather to engage in dialogue and diplomacy as an effort to resolve that."

Earlier in the day Kerry and Hagel had paid respects at Chidori ga Fuchi, Japan's national cemetery, in an apparent US attempt to nudge Japan away from lionising its controversial Yasukuni Shrine.

East Asian neighbours condemn Japanese leaders' visits to Yasukuni, which enshrines the remains of war criminals among other war dead.