Updated 16.55

Donald Trump has signed legislation imposing new sanctions on Russia, while also raising concerns about the bill.

The bill last month received overwhelming support from members of the US House of Representatives and Senate.

The legislation - which also imposes fresh sanctions on Iran and North Korea - comes amid continued investigations into Russia's alleged interference in last year's US election.

President Trump had reportedly weighed up vetoing the bill, which introduces a requirement that the White House must seek congressional review for any efforts to lift sanctions against Russia - a measure effectively limiting the president's powers.

In a statement, Trump said he signed the bill for the 'sake of national unity' despite his concerns with the legislation.

He argued: "The bill remains seriously flawed – particularly because it encroaches on the executive branch’s authority to negotiate. Congress could not even negotiate a healthcare bill after seven years of talking.

"By limiting the Executive’s flexibility, this bill makes it harder for the United States to strike good deals for the American people, and will drive China, Russia, and North Korea much closer together."

However, he also added: "[The bill] represents the will of the American people to see Russia take steps to improve relations with the United States. We hope there will be cooperation between our two countries on major global issues so that these sanctions will no longer be necessary."

Ahead of the official announcement, White House officials told outlets including The New York Times and Washington Post that President Trump signed the bill this morning. 

Even before it was signed into law, the new sanctions bill provoked retaliation from Russia.

Vladimir Putin announced over the weekend that he had ordered to US to cut 755 embassy and consulate staff over the coming months - more than 60% of the total staff. Reuters reports many of those likely to be let go will be Russian citizens.

Speaking on Russian television, President Putin said: "The American side has made a move which, it is important to note, hasn't been provoked by anything, to worsen Russian-US relations.

"[It includes] unlawful restrictions [and] attempts to influence other states of the world, including our allies, who are interested in developing and keeping relations with Russia,"