The nuclear negotiations remain stalled as the US says North Korea missed a December 31 deadline to provide a full inventory of its nuclear activities and facilities.
North Korea says it provided a list in November.
The US also suspects North Korea of continuing with secret uranium enrichment and of nuclear proliferation to Syria.
The US state department has played down the possibility of a breakthrough during the Singapore talks.
"I will be discussing the fact that we are kind of running out of time"
Christopher Hill, US nuclear envoy
But South Korean media reports have suggested that Kim Kye Gwan, North Korea's negotiator, may hand over a document that addresses concerns about its alleged secret uranium enrichment programme and co-operation with Syria.
There are expectations that Kim would "bring an answer acceptable to the US" with him to Singapore, Yonhap news agency quoted a South Korean foreign ministry official as saying.
The present round of difficult talks comes at a time of heightened tension on the heavily armed Korean peninsula after the North's missile tests and threat to attack the South.
Lee Myung-Bak, South Korean president, supported the nuclear negotiations on Tuesday.
"I hope the talks will be a success, paving the way for the settlement of the North Korean nuclear problem," he said.
North Korea's state-controlled media, however, continued its attacks on the South Korean president, who has been taking a less conciliatory approach to the North than his predecessors.
'Confrontation and war'
The Rodong Sinmun newspaper reported on Tuesday: "The manoeuvres by the Lee Myung-Bak clique to force the North to open, which are aimed at transforming our system and absorbing our republic into their so-called free democratic system, will bring nothing but confrontation and war."
From Singapore, Hill will go to Beijing, where he will meet the heads
of delegations of South Korea, Japan and China. He said he will also brief
the Russian ambassador to China.
North Korea began disabling its main nuclear facilities last year in exchange for aid and diplomatic concessions under an agreement with China, Japan, Russia, South Korea and the US under the six-party talks framework.