"And we think that the US is responsible for any eventualities... as far as China is concerned when it comes to the Taiwan issue," Fu said on the sidelines of the 10th Review Conference on the Treaty on Non-Proliferation of Nuclear Weapons (NPT) at the United Nations.
Pelosi led a US congressional delegation to the Indo-Pacific region and on Tuesday landed in Taiwan despite objections from Beijing.
The Chinese foreign ministry official also said "rest assured that there will be strong countermeasures against the US," for Pelosi's move.
Fu said China will try to resolve the issue via nonviolent means, but would not rule out the use of force.
"We will try our best to unite our country in a peaceful way. The reason why we do not give up the option of a military solution is because we need to deter those potential separatists and so that they will not go too fast," he added.
Beijing does not think nuclear weapons will be part of the picture over Pelosi's controversial visit to Taiwan, he added.
The Chinese official in addition said that the world situation is "quite tense," and more conflicts will be likely.
In addition, Fu said China urges the US, UK and Australia to halt development of the AUKUS alliance, which runs counter to the objectives of the NPT and IAEA statutes.
In terms of relations with Moscow, the Chinese foreign ministry official slammed the attempts by western countries to exclude Russia
With respect to nuclear arms control talks, Fu said Beijing hopes President Joe Biden's statements regarding starting dialogue with Russia on strategic stability are implemented. However, China refuses to join in any future talks.
"The US would use China as an excuse not to engage in further reduction or even run away from the New START Treaty. So China, categorically rejected that. It is a political game played by the Trump administration and China will not be participating in the political game," Fu said.
White House National Security Council spokesperson John Kirby this week said Pelosi's visit is not unprecedented and does not change US policy on Taiwan. The Biden administration has also said the visit does not provide a pretext for China to escalate tensions.