* North Korea restricts visitors from China
* Analyst says North concerned about reports on Kim's health
* North turns up heat on South's leader
By Jack Kim
PYONGYANG, Nov 13 North Korea looked to be further isolating itself, with reports on Thursday it was restricting travellers from major benefactor China and ignoring calls to lift a threat to close its border with the South.
The moves come a day after the North said it would not let international inspectors remove nuclear samples from its plant that produces weapons-grade plutonium, which could drag down an international disarmament-for-aid deal.
The measures came amid widespread speculation that North Korea's 66-year-old leader Kim Jong-il may have suffered a stroke, raising questions about his hold on power and who was making decisions about the country's nuclear weapons programme.
"By restricting the flow of Chinese visitors, North Korea seems to be trying to have a firmer grip on its internal situation, especially with Kim Jong-il's suspected health problems receiving global attention," said Park Young-ho, of the South's Korea Institute for National Unification.
China is the nearest North Korea has to a major ally and the rail and road routes across their border are the reclusive state's main commercial link to the outside world.
The Financial Times quoted U.S. officials as saying Beijing had increased the number of troops on its border with North Korea to prevent a possible flood of refugees flowing into China if leader Kim lost control.
"I haven't heard of any abnormal circumstances on the border between China and North Korea," Chinese Foreign Ministry spokesman Qin Gang said when asked about the reports of closing the border.
Travel agents in China, who send a steady though small stream of tourists to North Korea, said they were still organising visits, though trips had to be made via air rather than by rail.
China's relations with North Korea have long been characterised as being "as close as lips and teeth" after they fought side-by-side during the 1950-53 Korean War.
South Korea's Foreign Minister Yu Myung-hwan said the North may be trying to strong-arm the international community into giving it more aid in exchange for Pyongyang taking its foot off the brakes on the disarmament deal.
"If we consider North Korea's clear negotiation pattern, its strategy has always been to create a crisis before resolving something, and trying to use that point to secure further concessions," he told a seminar.
South Korea's top nuclear envoy was quoted as saying the North's move was effectively a rejection of a promise Pyongyang made last month to allow for checks of its nuclear claims.
NO RESPONSE FROM THE NORTH
North Korea reached a deal last month to resume disabling its Soviet-era Yongbyon nuclear plant and allow in inspectors to verify claims it made about its atomic arms programme after the United States removed it from a terrorism blacklist and rolled back trade sanctions.
The North has not responded to messages sent by the South calling for calm along the Cold War's last frontier and expressing regret over the threat to close the only border crossings between the Cold War rivals on Dec. 1, officials said.
The North's communist newspaper, however, turned up the heat on the South's President Lee Myung-bak who has ended what was once a free flow of unconditional aid.
"Traitor Lee's anachronistic 'policy towards the North' had already been thrown into the dumping ground of history," the Rodong Sinmun newspaper said in a commentary, calling on Lee to change course or risk increasing tension on the peninsula.
The North's moves on the nuclear deal came a little after Barack Obama met President George W. Bush at the White House and may serve as a reminder to the president-elect that Pyongyang expects to be taken seriously by the new administration, analysts said.
"North Korea doesn't want to be the top policy concern of the U.S. administration because that is too dangerous. But it always wants to stay somewhere in the top five," a diplomatic source in Seoul familiar with the North said. (Additional reporting by Kim Junghyun and Jon Herskovitz in Seoul and Ben Blanchard in Beijing; Writing by Jon Herskovitz; Editing by Jonathan Thatcher and Jeremy Laurence)