BEIJING - The World Health Organization (WHO) has warned that lifting restrictions too soon could lead to a deadly resurgence of COVID-19 as some countries are easing their social and economic restrictions amid the outbreak.

On Monday, WHO Director-General Tedros Adhanom Ghebreyesus told a virtual press conference from Geneva that a new strategy will be published to summarize what the world has already learned about the new virus.

"The decisions must be based first and foremost on protecting human health, and guided by what we know about the virus and how it behaves," he said.

The new strategy will include six criteria for countries which consider lifting restrictions:

First, transmission is controlled;

Second, health system capacities are in place to detect, test, isolate and treat every case and trace every contact;

Third, outbreak risks are minimized in special settings like health facilities and nursing homes;

Fourth, preventive measures are in place in workplaces, schools and other places where it's essential for people to go;

Fifth, importation risks can be managed;

And sixth, communities are fully educated, engaged and empowered to adjust to the "new norm."

"Every country should be implementing a comprehensive set of measures to slow down transmission and save lives, with the aim of reaching a steady state of low-level or no transmission," Tedros added.

On Friday, Tedros told a regular press briefing that a welcome slowing has been seen in some of the hardest-hit countries in Europe, like Spain, Italy, Germany and France.

As "some countries are already planning the transition out of stay-at-home restrictions," the WHO chief warned that "lifting restrictions too quickly could lead to a deadly resurgence."

"The way down can be as dangerous as the way up if not managed properly," he said, underlining that the WHO is working with affected countries on strategies for gradually and safely easing restrictions.

On Monday, workers from some non-essential sectors of the economy, mainly industry and construction, return to work in Spain, although experts warned of a possible new rise in coronavirus cases.

Spain's temporary ban on all non-essential work was imposed for two weeks by Prime Minister Pedro Sanchez on March 30, two weeks after imposing a State of Alarm and the corresponding lockdown on most of the population on March 14, in an attempt to halt the spread of the coronavirus.

The spread of the infection has slowed in Spain over the last month from around 20 percent on a daily basis to approximately 3 percent now. But the country had 169,496 confirmed cases and registered 17,489 deaths as of Monday. There are fears that allowing some people back to work will lead to a new rise in caseload.

In reality, reopening the economy will only affect a small percentage of the workforce, given that all shops (except those selling necessary items) remain closed, along with bars, restaurants, hotels, schools and cultural venues.

Meanwhile, many people have been adapted to home working over the past month and the fact that thousands of companies have opted to use a temporary regulation of work to lay off workers for the duration of the crisis will severely limit the number of workers returning to their posts on Monday.

In such Spanish regions as Catalonia, around 300,000 people will go back to work, mainly in the industrial and construction sectors.

The central government has issued guidelines advising workers to maintain distances of at least two meters between each other. Police were on duty in Madrid and other towns and cities on Monday morning to hand out face masks to those traveling on public transport.

Spanish Interior Minister Fernando Grande-Marlaska said the day was "developing within the normality of the exceptional situation which we are currently in."

"If the safety of workers is affected, then their activity cannot restart," he said.

However, not everyone agrees with the decision to reopen the economy. Daniel Prieto-Alhambra, a professor of epidemiology at Oxford University told Spanish national radio network RNE that the measure poses a "risk of new infections."

Also on Monday, three US West Coast states of California, Oregon and Washington, announced an agreement on a shared vision for reopening their economies and controlling COVID-19 into the future.

"We are announcing that California, Oregon and Washington have agreed to work together on a shared approach for reopening our economies -- one that identifies clear indicators for communities to restart public life and business," governors Gavin Newsom, Kate Brown, and Jay Inslee said in a joint statement.

The governors also pointed out that health outcomes and science, not politics, will guide their decisions.

"Through quick and decisive action, each of our states has made significant progress in flattening the curve and slowing the spread of COVID-19 among the broader public," according to the governors.

"COVID-19 doesn't follow state or national boundaries. It will take every level of government, working together, and a full picture of what's happening on the ground," said the governors.

There are more than 22,000, 1,500, and 10,000 confirmed cases of COVID-19 in California, Oregon and Washington respectively so far.

In Iran, President Hassan Rouhani said that the ban on inter-province travels placed to curb the spread of the novel coronavirus will be lifted on April 20, as Iran's daily infections decline, Financial Tribune daily reported on Monday.

During a meeting of the National Headquarters for Managing and Fighting the coronavirus, Rouhani said that restrictions on road trips across Iran's 31 provinces will be removed and low-risk businesses in the capital Tehran will resume activities later in April.

Following a decision by the Iranian authorities, all the low-risk business activities have reopened across the country except in Tehran since April 11.

The scheme allows some workplaces to reopen if they commit to complying with strict protocols of "a smart social distancing" introduced by the Health Ministry.

"The government is planning to make a decision on high-risk businesses" which requires mass gatherings, including gymnasiums, cinemas, beauty salons and stadiums as well, Rouhani added.

"High-risk businesses will resume work after careful analysis and planning," Rouhani was quoted as saying by Financial Tribune.

On Monday, Iraj Harirchi, Iranian Deputy Minister of Health and Medical Education, urged people to still remain at home and avoid any unnecessary trips, visits and shopping, despite the ease on social activities.

"Eighty percent of infected people have either little or no symptoms. These individuals can transmit the virus in society," Harirchi was quoted as saying by the state TV.

"Our efforts are aimed at identifying them in the early stages ... and to isolate those who have been in contact with such people," the official added.