(ATTN: REWRITES headline, lead; UPDATES with more info throughout, photo)
SEOUL, April 8 (Yonhap) -- U.S. President Donald Trump stressed the importance of the Seoul-Washington alliance and held in-depth talks over North Korea's nuclear problems during his summit with Chinese counterpart Xi Jinping, the office of South Korea's acting leader said Saturday.
Trump made the remarks during his 20-minute phone conversation with Acting President and Prime Minister Hwang Kyo-ahn which started at around 7:20 a.m. after his first summit with Xi.
"(Trump told Hwang) that there were in-depth discussions about North Korea's serious nuke problems and how to respond to them (during the summit)," according to Hwang's office.
"(The U.S. president said that) he delivered Washington's stance to China over the deployment of an advanced U.S. missile defense system in South Korea," it said.
The phone talks came after Trump and Xi agreed Friday to work together closely to convince North Korea to curb its nuclear program in their summit talks.
There is speculation that North Korea may carry out another nuclear test or launch a long-range rocket around its key anniversaries in April including the birthday of late founder Kim Il-sung on April 15.
Trump said he sufficiently emphasized to Xi the importance of South Korea and the Seoul-Washington alliance, the office said.
"(The U.S. President said that) during the summit, considerable time was spent in discussing issues of the Korean Peninsula," it said.
In response, Hwang stressed that South Korea and the U.S. should further strengthen close coordination against North Korea's possible provocations.
"I believe (the latest summit) seemed to be an occasion to reaffirm the strong alliance between Seoul and Washington," the acting president said.
Trump showed support for South Korea's policy toward North Korea, vowing close cooperation to resolve North Korea's nuclear standoff.
The summit also came amid China's strong opposition to Seoul and Washington's ongoing deployment of the Terminal High Altitude Area Defense (THAAD) on South Korean soil.
China showed an explicit objection to the THAAD installment, saying that the move undermines China's security interests.
The Seoul government viewed the latest phone talks as evidence supporting that high-level communication channels between the allies are smoothly working even in the midst of a leadership vacuum sparked by the ouster of former President Park Geun-hye.
Trump discussed North Korea's launch of a ballistic missile with Japanese Prime Minister Shinzo Abe over phone on Wednesday. But there were no phone talks with Hwang, sparking concerns that Seoul may be left out in discussion responses to Pyongyang's nuke and missile issues.
Meanwhile, the U.S. and China agreed on efforts to resolve North Korea's nuclear issue, but they did not go so far as to issue a joint statement in an indication that there was no major breakthrough over the matter.
"China has a red line which means that its employment of sanctions against North Korea should not be stringent enough to lead to North Korea's collapse," said Kim Hyun-wook, a professor at the Korea National Diplomatic Academy. "Washington seems to have failed to break China's threshold this time."
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