In July, Mr. Najib also shut down a newspaper, The Edge, because of its reports of payments between 1MDB and Mr. Low. On Monday, though, a court in Malaysia reversed the action, ruling that the paper could resume publication as soon as Tuesday. In a separate decision on Monday, a judge ruled that a lawsuit calling for Mr. Najib to return the money that had been transferred into his personal account, and for seizure of his assets around the world, could move forward.

All of that muddies Mr. Najib’s international standing as he prepares to fly to London this week for a trade convention and then on to New York for the opening of the United Nations General Assembly. Since taking office in 2009, Mr. Najib has drawn his country closer to the United States and has used his annual United Nations trips to promote Malaysia as a moderate Muslim partner in the fight against terrorism and as a strategic Asian counterforce to China.

“Najib really, really values his international image, and he was going out of his way to curry favor with America and with the Europeans,” said John Malott, a United States ambassador to Malaysia in the 1990s. In the current climate, he added, “he can travel, but is he going to be shunned? Are people going to shake hands with him?”

The $150 million in American properties tied to the prime minister’s stepson and to Mr. Low include a penthouse at the Time Warner Center at Columbus Circle in Manhattan purchased for $30.55 million by a shell company connected to Mr. Low’s family trust. Companies tied to Mr. Low’s family have also purchased a $39 million mansion on Oriole Drive in the Hollywood Hills in Los Angeles, the L’Ermitage Hotel in Beverly Hills and part of the Park Lane Hotel in New York. Through shell companies, Mr. Aziz purchased a $33.5 million condominium at the Park Laurel on 63rd Street in Manhattan, a home in Beverly Hills known as the pyramid house for a gold pyramid in its garden, as well as other properties in the Los Angeles area.

The Park Laurel condo and the Beverly Hills home were owned by shell companies connected to Mr. Low’s family before being transferred to shell companies tied to Mr. Aziz. Shell companies — trusts, limited liability companies and other entities — are commonly used in real estate for privacy, wealth transfer or shared ownership. They also make it difficult, however, for law enforcement authorities and others to discover the true owners of property.

In the case of the Beverly Hills home, the property was transferred without any public filings, with Mr. Low’s family trust selling ownership of the shell company to a corporate entity controlled by Mr. Aziz, The Times found.

Mr. Low’s spokesman said this year that the transfers to Mr. Aziz were done at fair market value and at arm’s length.