WASHINGTON (THE WASHINGTON POST) - When it comes to dealing with North Korea's nuclear weapons programme, many people hope sanctions are a useful tool. But not all sanctions are created equal.

The UN Security Council has voted unanimously to impose strict new sanctions on Pyongyang - a response to North Korea's launch of two intercontinental missiles last month.

The new measures significantly step up restrictions on North Korea's international trade: Estimates say it may cost Pyongyang US$1 billion (S$1.4 billion) a year, an enormous sum for a relatively poor country.

The hope is that these efforts may lead Mr Kim Jong Un's regime to abandon its nuclear weapons programme, or at least bring it to the negotiation table.

However, the effectiveness of sanctions is hard to predict - often it is difficult to quantify their effect even in hindsight - and North Korea's weapons programme has appeared relatively impervious to previous sanctions.

Here's an overview of the big questions about the new measures.

HOW ARE THE NEW SANCTIONS DIFFERENT FROM OTHER RECENT SANCTIONS?

North Korea has long been under sanctions. The UN Security Council imposed wide-ranging sanctions after Pyongyang conducted its first nuclear test, in 2006. The United States has imposed its own sanctions on Pyongyang, as have the European Union, South Korea and Japan.

In response to a missile launch last year, the Security Council passed Resolution 2270.

The harshest sanctions yet, these sweeping measures took the punishment a step further by targeting North Korean economic activity not directly related to proliferation, such as the export of mineral resources like coal or iron.

The new sanctions in Resolution 2371 largely expand upon these measures, such as broadening a cap on coal and iron exports to a full-fledged ban and adding new restrictions on things such as seafood exports and the use of North Korean labourers abroad.

Notably, it appears to remove parts of the old sanctions that aimed to avoid "adverse humanitarian consequences" for civilians, Mr Benjamin Katzeff Silberstein, an associate scholar at the Foreign Policy Research Institute, observed at the North Korean Economy Watch blog.

"In sum, the new resolution appears much more holistic than its predecessors in fully cutting off North Korea's most central export revenues," Mr Katzeff Silberstein wrote.

The effect of such sanctions could be big: The aim is cut off a third of North Korea's estimated US$3 billion in annual exports.

However, the new sanctions will still rely on implementation from UN member states, which has proven to be problematic in the past.

WHY IS IT IMPORTANT THAT CHINA AND RUSSIA WERE INVOLVED?

On Twitter, President Donald Trump has singled out Russian and Chinese support for the new sanctions: "The United Nations Security Council just voted 15-0 to sanction North Korea. China and Russia voted with us. Very big financial impact!"

Getting China and Russia on board for sanctions is certainly important. Both are major economic partners of North Korea, so if they apply pressure, it will be felt in North Korea.

But it is perhaps not quite as simple a victory as Mr Trump portrays it to be.

Both China and Russia supported the Obama-era UN sanctions agreed upon last year, but critics contend that the two countries have not done enough to limit their economic relationship with North Korea.

Earlier this year, Russia expanded its use of North Korean migrant workers. Notably, while the new sanctions prohibit any increases in the number of these migrant workers, they do not call for those already abroad to be sent back.

Mr Troy Stangarone of the Korea Economic Institute of America suggests that these workers could end up sending more money home if their wages were to increase.

Meanwhile, it took months for China to make any effort to meet last year's UN cap on coal imports from North Korea, and there remain major questions about whether the trade figures it released publicly are truthful.

Even if the figures on coal imports are accurate, they do not appear to have negatively affected the booming China-North Korea trade overall - despite frequent warnings from the Trump administration.

WILL THESE NEW SANCTIONS WORK?

There is little doubt that the new sanctions are a rare diplomatic success for Mr Trump. However, that does not necessarily mean they will work as intended. Many experts doubt that they will truly be effective if not fully enforced.

"The US$1 billion number depends on China implementing the UN sanctions," Mr Anthony Ruggiero, a senior fellow at the Foundation for Defence of Democracies and a former US Treasury official, wrote on Twitter on Sunday. "We only have 11 years of evidence they will not do so."

Both China and Russia share a border with North Korea and remain deeply worried about the prospect of economic chaos in that country.

Russia's state media quoted the country's UN ambassador Vasily Nebenzya as saying on Saturday that sanctions "shall not be used for economic strangling" of North Korea.

Notably, the new sanctions do not cut off North Korean crude oil imports, thought to be a major part of China and North Korea's economic relationship.

A bigger problem may be that even if the sanctions are implemented fully, they still may not produce the desired effect.

In the past, North Korea has used sanctions as a domestic propaganda tool and an excuse for its own economic mismanagement. Resolution 2371 explicitly mentions this, with language expressing regret for Pyongyang's "massive diversion of its scarce resources towards its development of nuclear weapons and a number of expensive ballistic missile programmes".

Moreover, North Korea's leadership clearly views its nuclear weapons programme as central to its long-term survival - and perhaps loftier and ideologically driven desires to unite the Korean Peninsula. The country has weathered economic disaster before and found inventive ways to flout trade restrictions.

Pyongyang's weapons programme also has made some major leaps in the past year, and US officials believe that it may be able to produce a reliable, nuclear-capable intercontinental ballistic missile by 2018.

At this late stage, persuading North Korea to halt or abandon this programme will be difficult.

Secretary of State Rex Tillerson has admitted that there will be a lag time before the sanctions "actually have a practical bite on their revenues", further limiting the pressure.

For its part, North Korea has not offered much contrition. "We will make the US pay by a thousand-fold for all the heinous crimes it commits against the state and people of this country," a statement published on Monday in the state-run Korean Central News Agency read.