Mattis' comments drew a pointed reaction from a Chinese official at the meeting.
Beijing's deployments of missile batteries and bombers to outposts in disputed areas appear aimed at intimidating neighbours, Mattis told delegates on Saturday at the International Institute for Strategic Studies (IISS) Shangri-La Dialogue in Singapore.
Mr Mattis, speaking at the annual Shangri-La Dialogue summit in Singapore, said: "Despite China's claims to the contrary, the placement of these weapon systems is tied directly to military use for the purposes of intimidation and coercion".
He added there would be "consequences" if China does "not find the way to work more collaboratively with all of the nations who have interest".
On the sidelines of the Singapore conference, Lieutenant General He Lei of the China's PLA Academy of Military Sciences said China had every right to continue to militarise its South China Sea holdings.
"Any irresponsible comments from other countries can not be accepted", Lieutenant General He Lei said at the Shangri-La Dialogue in Singapore.
The comments came on the heels of a string of events that highlight the tension between the world's two biggest economies over the South China Sea's disputed waters.
China's air force has landed long-range military aircraft on an island in the disputed South China Sea, a move that is believed to be the first of its kind and is likely to fuel further concerns about Beijing's intentions in the region.
China defended today its right to deploy troops and military camps in the South Sea islands under its juridiction in response to critizism from the United States in that matter.
Last week, two U.S. Navy vessels also sailed near China-controlled islands in what Mattis called "an affirmation of the worldwide rules-based order".
Migrant Children At The Border
Former GOP Senator from Pennsylvania Rick Santorum even tried placing the blame on the children's parents . During President Barack Obama's second term, the government prosecuted roughly 70,000 cases per year.
But he also said the US welcomes cooperation with China "wherever possible", and announced that he has accepted Beijing's invitation to visit soon.
France and the United Kingdom will challenge Beijing by sailing through contested waters in the South China Sea.
The South China Sea, a key trade route, is subject to overlapping claims by China, Vietnam, the Philippines, Malaysia, Taiwan and Brunei. But while other countries have built military features and artificial islands, none come close to matching Beijing's in scale or ambition, which stretch hundreds of miles south and east from its most southerly province of Hainan.
He did however, seek to calm nervous allies in the region.
Mattis also touched on Taiwan, a longstanding dispute between the USA and China. -China relations, as the Trump administration is warily asking for China's help with North Korea ahead of a June 12 summit, while also threatening a trade war.
Although France is not a claimant in the South China Sea dispute, by conducting such exercises "on a regular basis with allies and friends" it is contributing to a rule-based order, according to Parly.
"I don't see what options Australia's got beyond a vigorous diplomatic assertion and what options America has got beyond continuing freedom of navigation patrols perhaps on a more regular rotation than what's happening now".
Mattis emphasized that the US military wants more transparency from China.
"We've been sending a clear message to all that the freedom of navigation is absolutely critical", he said.
Trump's absence from the public eye has prompted reactions, including jokes and conspiracy theories, from many social media users. The first lady remained in the hospital for five nights following the procedure prior to returning to the White House on May 19.
Fortnite's availability on the Nintendo Switch should only add to the hordes of cash that Epic Games is pulling in from the title. Nintendo has shied away from such games on its consoles in the past, but now appears to be open to the popular games.
In a tense encounter, both men were slapped with code violations for coaching before Cecchinato gallantly saved three set points. Thiem took the first set with just a solitary break of serve which he sealed with a brilliant cross-court backhand.
He missed a 3-foot birdie putt on the ninth hole, and then missed a birdie putt from 4 feet on the par-5 15th. He hit a flop shot to a few feet and was certain to get par when DeChambeau ended it with his birdie putt.
On Coutinho's first return to Anfield, it was noticeable how much he was whistled by sections of the crowd. And Neymar needed just 23 minutes to prove how important he is to Brazil's hopes of a sixth world title.
Trump said on Friday he might prefer to end NAFTA in favor of separate bilateral agreements with the two US neighbors. The group includes Canada , France, Italy, Germany, the United Kingdom, Japan and the United States.
The euro might survive an Italian exit, but it would "put Italy, the euro area economy and the European Union in deep distress". Earlier it fell to $1.1510, its lowest level since last July before recovering to trade 0.5 percent down on the day at $1.1565.
Lionel Messi was No. 2 at $111 million, followed by Ronaldo at $108 million, McGregor at $99 million , and Neymar at $90 million. Lionel Messi and Cristiano Ronaldo complete the podium with $111M and $108M respectively.
But cut to the next day, he met a North Korean official at the White House and pointed out that the summit was back on track. That means Trump needs to get something tangible out of a summit that will draw intense global scrutiny, analysts said.
The woman has spent more than two decades behind bars and now resides in Alabama's Aliceville Federal Correctional Institution. The meeting took place following two American criminal justice developments at the White House over the last few weeks.
Trump lawyer says Kim begged for meeting
On June 4, President Trump tweeted he has "the absolute right" to pardon himself but added that he has "done nothing wrong". Giuliani said during an appearance on CNN that "it was a mistake" and rejected the idea that it was a lie.
Serena Williams Withdraws From French Open With Arm Injury
In my doubles yesterday I tried lots of different tapings. "I thought [doubles] was a ideal opportunity to see how I was going". The athlete said she first noticed chest pain during a victorious match against Julia Görges on Saturday, June 2.
Dzumhur gives hungry Zverev food for thought
In the women's draw, Australian Open champion Caroline Wozniacki eased past Frenchwoman Pauline Parmentier 6-0, 6-3. Late breaks in both sets gave the Bosnian the win as he reached the semifinals in China a 6-4 7-5 victor .
Serena Williams makes fashion statement in Grand Slam return
But from somewhere Williams got her serve firing and summoned up her powerful groundstrokes to blow Barty away 3-6 6-3 6-4. Barty put up a stiff challenge, and really forced Serena out of her comfort zone with a mix of slices and topspin shots.