US Secretary of State Antony Blinken arrived Sunday in South Korea on the first stop of a brief Asia tour also including the Philippines, as Washington moves to reinforce ties with two key regional allies.

Blinken landed Sunday afternoon ahead of the third Summit for Democracy on Monday, an initiative of US President Joe Biden, which Seoul is hosting this week.

Before arriving in Seoul, Blinken made a brief stop in Bahrain, where he spoke to King Hamad bin Isa Al-Khalifa about efforts to achieve a ceasefire in Gaza.

The summit, which runs from March 18-20 will bring together government officials, NGOs and civil society members.

Seoul is one of Washington's key regional allies, and the United States has stationed about 27,000 American soldiers in the South, to help protect it against the nuclear-armed North.

Seoul's conservative President Yoon Suk Yeol has boosted ties with Washington and sought to bury the historical hatchet with former colonial power Japan to better guard against Pyongyang's threats.

Blinken will meet South Korean Foreign Minister Cho tae-yul, the ministry said, for discussions that will cover how to boost the alliance, as Washington and Seoul explore how to improve their so-called "extended deterrence" against North Korea.

The democracy summit has attracted some criticism due to its selective invitation list, which excludes countries that consider themselves democratic, such as Thailand and Turkey.

After Seoul, Blinken heads to Manila, a trip that will reaffirm "our unwavering commitment to the Philippine ally", according to State Department spokesperson Matthew Miller.

He will talk with local officials including President Ferdinand Marcos, with issues with China including over the South China Sea likely to top the agenda.

The US is redoubling efforts to improve longstanding ties with regional allies such as Manila, in an effort to counterbalance China.

Beijing recently accused Washington of using the Philippines as a "pawn" in the dispute over the South China Sea, after a series of clashes around bitterly-contested islets in the waters.

China claims almost the entire waterway, brushing aside competing claims from a host of Southeast Asian nations and an international ruling that has declared its stance baseless.

The South China Sea is strategically vital for several countries -- including China -- providing a key route for the import and export of essential fuel, food and other goods.

China has rapidly grown its naval forces in recent years, and snatched vast tracts of maritime territory, hoping to project its military and political power well beyond the country's shores.