Taiwan's opposition presidential candidate has assured the United States she would not whip up tensions with China if elected but pledged to boost defense spending to counterbalance a rising Beijing.

The United States, the primary guarantor of the island's security, has repeatedly hailed the easing of tensions across the Taiwan Strait since voters elected Beijing-friendly President Ma Ying-jeou in 2008.

On a visit to Washington on Tuesday, Tsai Ing-wen -- who is challenging Ma in January elections -- acknowledged a "rough period" between Taiwan and the United States when her Democratic Progressive Party was last in power.

But Tsai said the DPP -- which emphasizes Taiwan's separate identity from mainland China and in the past has flirted with declaring independence -- has "matured along with the development of Taiwan's democracy."

"The DPP's approach towards China will be stable and balanced," Tsai said at the American Enterprise Institute, a conservative think-tank.

"Our policy must be in line with the mainstream consensus in our society as well as international expectations and therefore we will refrain from extreme or radical approaches," she said.

Tsai, however, criticized Ma for a "lack of dedication to a strong defense."

While calling for the United States to sell fighter jets to the island, Ma has not met a goal of devoting three percent of GDP to military spending, saying that the global economic crisis necessitated other priorities.

"When we come back to government, the situation must be rectified by a stronger demonstrated commitment," Tsai said.

China claims Taiwan as part of its territory awaiting reunification. The mainland's nationalists fled to the island in 1949 after losing the civil war and it has since turned into a vibrant, self-governing democracy.

The United States recognizes only China but under a 1979 law is required to provide for the island's defense. President Barack Obama's administration in January 2010 approved $6.4 billion in arms to Taiwan, angering China.

But the administration has refrained from selling the island the latest F-16 fighter jets, despite rising pressure from Taiwan's supporters in the US Congress and assessments that China is gaining a military edge.

Tsai also called for the jets, saying: "We urge you to make a decision to provide us with the necessary weapons, but at the same time we ourselves have to make the determination that we want to defend ourselves."

The DPP has sharply criticized a Taiwan-China free trade agreement -- one of Ma's signature achievements -- saying that it could lead to Beijing's domination of the island by non-military means.

But Tsai said that as the deal is already signed, the party would consider revisions only through "democratic procedures."

US diplomats were often uneasy about Ma's DPP predecessor Chen Shui-bian, who infuriated the mainland with moves such as abolishing a largely symbolic office that was meant to study reunification.

Ma's aides are also visiting Washington, delivering a message that another term for the incumbent would serve US interests.

"President Chen stirred up crisis after crisis across the Strait, compromised our relations with the United States and also other allies," said Francis Yi-hua Kan, deputy director for international affairs of Ma's presidential campaign.

"We do not want to repeat that mistake. We first need to reduce the tensions so that the US has more leverage to deal with other issues. We have lots of problems around; we don't want to create another," he told AFP.

Tseng Yung-chuan, the deputy speaker of parliament and member of Ma's Kuomintang, said that the Obama administration's support for lower cross-strait tensions would have "a positive impact on our current election."

But he said that Taiwan "will feel regret" if the United States does not sell the F-16s.

Tseng called for the Obama administration to make more gestures, such as relaxing rules to allow Taiwanese to visit the United States without visas.