Pyongyang Getting Pinched

North Korea, already one of the world's most isolated countries, is looking even lonelier these days, squeezed not only by its adversary the United States but also its friends in Beijing.

China said Monday that its military has taken over patrolling its frontier with North Korea, but wouldn't disclose why it made the change.

The U.S. military said Tuesday it has enhanced its air defense system in South Korea to better counter missile threats from the North. The United States will increase efforts to halt heroin and other drug trafficking linked to North Korea, the White House said.

And the United States is reviewing whether or not to send North Korea the remaining 66,000 tons of food aid due this year out of concern the food might not get to people who need it, the State Department said Monday.

All that comes after nearly a year of tension over North Korea's nuclear program.

The Chinese Foreign Ministry would not confirm reports in Hong Kong media that China moved 150,000 troops to the border to stem crime by North Korean soldiers and to pressure its isolated communist neighbor to halt its nuclear weapons program.

"It is a normal adjustment carried out after many years of preparation by the relevant parties," the Chinese Foreign Ministry said in a brief statement.

It wasn't clear which agency previously patrolled the border, which is off-limits to foreign reporters. But such duties are believed to have been held by the People's Armed Police, a paramilitary force also run by the Defense Ministry.

U.S. and South Korean analysts, who said they couldn't confirm the troop movements, disagreed over whether Beijing would take such a step to pressure its longtime ally.

A U.S. official, speaking on condition of anonymity, said the Chinese have been reorganizing border forces for about a year, replacing border guards with army troops to increase security along its frontier, including the North Korean border, and the move does not appear to be linked to a specific issue.

China fought alongside North Korea in the 1950-53 Korean War and is the isolated North's main aid supplier. But diplomats and scholars say the North has angered China by declaring it had nuclear weapons and resisting U.S. pressure to scrap its weapons programs.

Beijing has tried unsuccessfully to mediate the weapons dispute. A second round of talks in August ended without agreement or a date for more negotiations.

David M. Lampton, director of China studies at the Johns Hopkins School of Advanced International Studies in Washington, said China has been "ratcheting up the pressure" on the North — especially since it said in April that it already had a nuclear weapon.

"I wouldn't be surprised if China" moved troops to the border, Lampton said. "This could be an attempt to show that China won't be intimidated."

But Baek Seung-joo of South Korea's government-run Korea Institute for Defense Analysis was skeptical about possible Chinese attempts at military pressure.

"Considering the relations between China and North Korea, it is difficult to imagine that China would use its military as a means to influence North Korea," said Baek, leader of the institute's North Korea research team.

Sing Tao said the troops also were meant to stem cross-border crime by North Korean soldiers and the flow of refugees fleeing repression and hunger in the North.

China has been frustrated and embarrassed by the refugees, who are believed to number in the tens of thousands. Nearly 200 have been allowed to leave for rival South Korea after seeking asylum in embassies and other foreign offices.

Meanwhile, the U.S. military has received new equipment to upgrade its system to the latest generation of Patriot interceptor missiles, the Patriot Advanced Capability-3, the Eighth U.S. Army said in a news release.

The Patriot missiles are built to destroy targets — such as tactical ballistic missiles, cruise missiles and enemy aircraft — by colliding with them at high speed, rather than using an explosive warhead.

"This system enhances our ability to prevent any external aggression which includes North Korea," said Lt. Col. Steven Boylan, a spokesman for the Eighth Army.

North Korea has an aggressive missile development program, although most of its 1.1-million army is equipped with outdated Soviet-era weapons. Its Rodong missiles can reach all of South Korea and much of Japan.

White House Press Secretary Scott McClellan said Monday, in a statement accompanying a government report on narcotics trafficking, that Mr. Bush "registered his growing concern over heroin and methamphetamine trafficking linked to North Korea and expressed his intent for the United States to intensify its efforts to stop North Korean involvement in narcotics production and trafficking."

At the State Department, spokesman Adam Ereli said Monday that the United States is reviewing whether to send North Korea the final 66,000 tons of food aid due this year. He said the government in Pyongyang has placed restrictions on the U.N. World Food Program, which distributes humanitarian aid in North Korea, that do not allow the WFP to ensure the aid gets to "vulnerable North Koreans."

So far this year, Ereli said, the United States has provided 44,000 tons of its 110,000-ton commitment to North Korea.

The nuclear tensions began last October when North Korea said it was enriching uranium. The U.S. cut off fuel supplies, and Pyongyang pulled out of the Nuclear Nonproliferation Treaty. At recent talks, North Korea threatened to conduct a nuclear test.