While China won't be participating in next Tuesday's nuclear summit between President Trump and North Korean leader Kim Jong Un, US officials say they are preparing to counter a wide variety of spying techniques employed by Beijing at the Capella Hotel on the resort island of Sentosa, Singapore, reports NBC News.

“China remains a particularly aggressive espionage actor and is using increasingly sophisticated technological platforms to carry out its objectives,” said Dean Boyd, spokesman for the National Counterintelligence and Security Center, a new counterintelligence agency established under the DNI.

China has employed aggressive espionage techniques in recent years - bugging everything from hotel keys to jewelry, which likely include the "friendship pins" given to White House officials during a visit to Beijing last November.

During the visit, the officials say the Chinese gave the U.S. delegation pins that the Americans called their friendship pins. But members of the delegation were not allowed to wear the pins into a secure area because security officials warned they likely had embedded listening devices. The officials said their belongings were rifled through while they were not in their hotel rooms, as happened to U.S. officials during previous presidential trips to China. Some senior members of Trump’s delegation packed carry-on bags with anything they didn’t want the Chinese to see and took the bags wherever they went, including out to dinner in restaurants, according to officials. -NBC News

Of particular concern ahead of the summit via NBC News:

U.S. officials are concerned China has recruited informants among the waiters and other staff in Singapore’s restaurants and bars, who are paid to eavesdrop on American customers and report back to their Chinese handlers.

Officials also expect electronic surveillance of the summit meeting sites. Americans will sweep for bugs in rooms at the Capella Hotel that could be used for side discussions, and could erect tents inside hotel meeting rooms to block any concealed cameras from viewing classified documents.

Chinese intelligence agencies have shown the ability to penetrate mobile phones even when they are off, and U.S. officials are now told to take their batteries out when they are concerned about eavesdropping, according to a U.S. intelligence official.

"Chinese intelligence collection could be amped up around the summit," said Jeremy Bash, former Chief of Staff to CIA Director Leon Panetta. "They have prioritized surveillance in recent years and their technical prowess has really advanced."

According to three U.S. officials, in one recent case a top U.S. official working in China repeatedly had trouble with his hotel key card. He had to replace it several times at the front desk because it wouldn’t open his door. He brought one of the key cards back to the U.S., where security officials found a microphone embedded inside, according to the U.S. officials. The Chinese have placed listening and tracking devices in chips embedded in credit cards, key chains, jewelry, and even event credentials, the officials said, often with the intent of capturing secret conversations among American officials. -NBC News

Cell phones are particularly vulnerable. Following President Obama's 2009 trip to China, one of his national security advisors was forced to throw away a Blackberry device because the Chinese were able to crack into it, according to a former administration official. Meanwhile President Trump uses two unsecured iPhones; one for talking and one for tweeting.

The president, who relies on cellphones to reach his friends and millions of Twitter followers, has rebuffed staff efforts to strengthen security around his phone use, according to the administration officials. The president uses at least two iPhones, according to one of the officials. The phones — one capable only of making calls, the other equipped only with the Twitter app and preloaded with a handful of news sites — are issued by White House Information Technology and the White House Communications Agency, an office staffed by military personnel that oversees White House telecommunications. -Politico

Meanwhile, the Washington Post reported this week that the Department of Homeland Security confirmed that a a device used to eavesdrop on cell phones and other electronic devices was detected near the White House, prompting concerns that it may have been used to spy on key government officials

Last Saturday, a former Defense Intelligence Agency (DIA) officer, Ron Rockwell Hanson, 58, was arrested Saturday afternoon on 15 federal charges, including the attempted transmission of national defense information to the People's Republic of China, according to the Department of Justice (DOJ).

Hanson, a resident of Syracuse, Utah, was taken into custody while he was on his way to Seattle-Tacoma International Airport in Seattle before boarding a connecting flight to China. Hanson's arrest comes on the heels of a January incident in which ex-CIA officer Jerry Chun Shing Lee, 53, was arrested at New York's John F. Kennedy airport and indicted in May on charges of spying for China.

US government employees in China are instructed to presume that their residenced are all wired for sound and video, and that the Chinese are recording everything they do, according to NBC. Officials are also briefed on hotel room security. In 2008, the State Department issued a fact sheet for Americans traveling to the summer Olympics in Beijing, stating that there would be no reasonable expectation of privacy in public or private locations.

"China poses the most sophisticated counterintelligence threat to the U.S. of any other country right now,” said Bash. “And their intelligence gathering is probably at its highest peak in a long time."