Beijing urged Washington on Tuesday to keep its promises and stop arms sales to Taiwan.

A US Republican congressional aide said on Monday the Obama administration is expected - possibly this week - to authorize the sale of two guided missile frigates to Taiwan, Reuters reported.

At a news briefing on Tuesday, Chinese Foreign Ministry spokesman Hong Lei said China firmly opposes US arms sales to Taiwan and "strongly urges the US to be fully aware of the high sensitivity and serious harm of the issue".

Hong said US arms sales to Taiwan interfere with China's internal affairs and violate three China-US joint statements. The arms sales are particularly at odds with the principles specified in the August 17 Communique signed in 1982, under which the US agreed to gradually reduce such sales to Taiwan and indicated that they would eventually stop.

The US must end the sales "to avoid damaging China-US relations and the peaceful development of relations across the Taiwan Straits," Hong said.

Washington's arms sales are sanctioned by the US government's Taiwan Relations Act, which Beijing has long described as a "cancer" in Sino-US ties. The proposed latest sale would be the first in four years, the longest gap in such sales for nearly four decades.

In December last year, the US Congress passed the Naval Transfer Act authorizing the sale of up to four Perry-class frigates to Taiwan.

Taiwan has said it expects to pay about $176 million for the two vessels and that it would review its needs before making a decision on two more.

Many Chinese regard it as making no sense or even humiliating for US to sell arms to Taiwan when cross-Strait relations have been peaceful and the fact that the US is arming a place, which is part of China.

US arms sales to Taiwan, its close-in military surveillance off China's coast and the US Congressional laws restricting military exchanges and cooperation between China and the US have long been called by China as the three major stumbling blocks for developing healthy military-to-military relations.

Yu Qiang, a leading expert on the Taiwan issue at the University of International Relations in Beijing, said Washington would still be using the Taiwan question as a tool to contain China if it goes ahead with the sale.

"If the United States insists on arms sales to Taiwan, it will not only harm Sino-US ties and cross-Straits relations, but also cast doubt on its commitment of not seeking to contain China," Yu said.

Zhiqun Zhu, professor of political science and international relations and director of the China Institute at Pennsylvania-based Bucknell University, said the US arms sale to Taiwan remains an irritant in US-China relations, but is unlikely to destabilize the bilateral relationship.

"It is more symbolic of US commitment than substantive -- for example, Taiwan will not get the more advanced weapons it desires for such as F-16C/Ds," Zhu said.

Zhu described the move as part of US domestic politics, particularly the tug of war between the legislative branch and the executive branch. "That it has been four years since the last sale is also telling."

Reuters contributed to the story.

Contact the writer at wangxu@chinadaily.com.cn or chenweihua@chinadailyusa.com

wangxu@chinadaily.com.cn