Defense Ministry spokesman Ren Guoqiang also said the sides remain in contact over a possible visit to China by U.S. Defense Secretary Jim Mattis at a date yet to be announced.
The United States is considering intensified naval patrols in the South China Sea to counter what it sees as China's militarization of the strategic waterway, a move that could further increase tensions with Beijing, officials say.
Gen Mattis said the Trump administration wanted a constructive relationship with China but would compete vigorously if necessary.
China has deployed anti-ship missiles, surface to air missiles and other military equipment on the disputed Spratly Islands and Woody Island.
"It's for the sake of defending ourselves", he added, and warned Beijing would take "agency measures" if different global locations despatched ships and plane near what it considers its islands within the South China Sea.
"When it comes down to introducing what they have done in the South China Sea, there are consequences", said Mattis.
Last week the USA withdrew an invitation for Beijing to participate the exercise known as Rim of the Pacific.
He then warned that "there are consequences that will come home to roost if they don't find a way to work collaboratively with neighbours who have interests".
"By exercising our freedom of navigation, we also place ourselves in the position of a persistent objector to the creation of any claim to de facto sovereignty on the islands", Parly added.
He Lei heads China's delegation at an annual security summit in Singapore.
China's hostility towards self-ruled Taiwan has grown since Tsai Ing-wen from the pro-independence Democratic Progressive Party won presidential elections on the island in 2016. Taiwan claims the same area as China.
Mr Mattis also said the issue of USA troops in South Korea was "not on the table" at this month's summit with North Korea's Kim Jong-un. And he says the US remains committed to ensuring free and open transit in the region.
The French Minister of Defense, Florence Parly, said she welcomes the signs of dialogue, but added that sanctions should continue until denuclearization is achieved in a full, verifiable and irreversible manner. Mattis characterised this action as an "initial response".
Despite He's admission, he batted back Mattis' accusations, saying that the "close-up reconnaissance" carried out by two United States warships - which sailed within 12 nautical miles of the Paracel Islands last week - was the real "source of militarisation" in the region.
He said Asia can only prosper under the rule of law, and stressed the importance of a rule-based worldwide order.
Japan's Defense Minister Itsunori Onodera, who also spoke at the forum, said it was important not to reward North Korea for only agreeing to dialogue.
"We did not do freedom of navigation for America alone", Mattis said.
This year, the summit focused its discussions on the challenges to security in the Indo-Pacific region, the maritime region centred around Southeast Asia. "Certainly we have had some unusual approaches, I'll be candid with you", Mattis replied.
"It would be a lose-lose scenario for the world if the US and China are unwilling to work together for an inclusive system that both large and small states can benefit from, and where rules apply to all", Ng said.