The government of Qatar bought a $6.5m apartment in one of Donald Trump’s New York towers soon after the dismissal of a lawsuit that tried to stop the president benefiting from such deals.

Qatar’s mission to the United Nations signed a deal for the condominium at Trump World Tower on 17 January, according to city records. The purchase means that the Middle Eastern state now owns four units in the building, for which it paid $16.5m.

On 21 December, a federal judge in New York had thrown out a lawsuit from ethics campaigners alleging that Trump was breaching the emoluments clause of the US constitution by collecting tens of thousands of dollars in charges from Qatar each year for the three apartments it already owned in the building.

Qatar’s new acquisition at Trump World Tower, which is in Manhattan’s Midtown East section, coincided with an intense lobbying campaign in Washington by the Qatari government amid a regional crisis that has pitted the Gulf monarchy against Saudi Arabia and the United Arab Emirates.

Jordan Libowitz, a spokesman for Citizens for Responsibility and Ethics in Washington (Crew), which brought the lawsuit against Trump, said: “This plays to the central concern with the president’s refusal to divest from his holdings – that he would be susceptible to influence from foreign countries invested in his businesses.”