Speaking at an Asian regional forum on security, Xi said a rising China would seek "peaceful" means to resolve territorial disputes.
Beijing has sought to counter Washington's foreign policy "pivot" to Asia, but it has also irritated Vietnam, Japan and the Philippines -- the latter two allies of the US -- with what those countries say are aggressive moves in separate territorial disputes.
"To beef up an entrenched or military alliance targeted at a third party is not conducive to maintaining common security," Xi said, without naming names.
Washington's traditional allies in the Asia-Pacific region include Japan, where it has military bases and whose security it guarantees by treaty, and Australia.
China's official Xinhua news agency on Tuesday urged countries from outside Asia not to foment tensions.
"Players from other parts of the world need to play a constructive role. They should refrain from starting fires and stoking flames," it said in an editorial.
Relations between China and Vietnam have worsened after Beijing sent a deep-water oil drilling rig into contested waters in the South China Sea earlier this month, sparking violent Vietnamese protests in which at least two Chinese were killed.
China and Japan have a long-running feud over disputed islands in the East China Sea, while the Philippines accuses China of reclaiming land on a disputed reef within its exclusive economic zone under a United Nations convention.
But Xi said: "China stays committed to seeking peaceful settlement of disputes with other countries over territorial sovereignty, and maritime rights and interests."
He was speaking at the Conference on Interaction and Confidence Building Measures in Asia (CICA), a relatively obscure forum which exists alongside other more prominent regional groupings.
Vietnam belongs to the forum, but Japan is only an observer while the Philippines is not a member. The United States has observer status, preferring to work through the Asia-Pacific Economic Cooperation (APEC) forum.
- Push to assert interests -
Xi, who became president last year, has overseen a foreign policy which has sought to assert China's interests in both continental Asia and the Pacific Ocean.
He told the forum that China was interested in a regional security code, but gave no details.
Earlier this month, Southeast Asian leaders expressed "serious concern" over worsening territorial disputes in the South China Sea, calling for a peaceful resolution and presenting a rare united front against Beijing.
Several countries have overlapping claims in the South China Sea, which is home to key shipping lanes and thought to contain vast energy reserves.
Before the start of the forum, Xi shook hands with other state leaders attending, including Russia's Vladimir Putin, Hassan Rouhani of Iran and Afghanistan's Hamid Karzai.
But the live television broadcast appeared to cut away when Vietnamese Vice President Nguyen Thi Doan shook hands with Xi.
The move by China's heavily-censored state television drew some laughter from Chinese journalists in the media centre, with one saying: "You can't see that."
On Tuesday, Xi and Putin launched naval exercises off Shanghai and held talks but failed to seal a long-awaited deal for Russia to export natural gas to an energy-hungry China.
Analysts said China is trying to raise the importance of the conference, which in some respects competes with APEC and the Association of Southeast Asian Nations (ASEAN).
"Everyone is a bit surprised it's being made such a big deal," said Raffaello Pantucci, research fellow at the Royal United Services Institute for Defence and Security Studies.
"It's more about China trying to build their regional relationships... in a part of the world where they've made a very active push," he said.