BERLIN (AP) – The World Health Organization says there is “no public health justification” for postponing or canceling the Rio Summer Olympics because of the Zika outbreak in Brazil.

The assessment, in a statement early Saturday, came a day after 150 health experts issued an open letter to the U.N. health agency calling for the games to be delayed or relocated “in the name of public health.”

Friday’s letter cited recent scientific evidence that the Zika virus causes severe birth defects , most notably babies born with abnormally small heads. In adults, it can cause neurological problems, including a rare syndrome that can be fatal or result in temporary paralysis.

The authors also noted that despite increased efforts to wipe out the mosquitoes that spread Zika, the number of infections in Rio de Janeiro have gone up rather than down.

The experts came from more than two dozen countries in fields including public health, bioethics and pediatrics, and included former White House science adviser Dr. Philip Rubin.

WHO, however, said “based on current assessment, cancelling or changing the location of the 2016 Olympics will not significantly alter the international spread of Zika virus.”

Several public health academics have previously warned that having hundreds of thousands of people travel to the Aug. 5-21 games in Brazil will inevitably lead to the births of more brain-damaged babies and speed up the virus’ global spread.

But the Geneva-based U.N. health agency argued that Brazil is just one of dozens of countries reporting the transmission of the Zika virus by mosquitoes and says “people continue to travel between these countries and territories for a variety of reasons.”

“Based on the current assessment of the Zika virus circulating in almost 60 countries globally and 39 in the Americas, there is no public health justification for postponing or cancelling the games,” it said. “WHO will continue to monitor the situation and update our advice as necessary.”

It pointed to its existing advice urging pregnant women not to travel to areas with Zika virus transmission, among other recommendations.

WHO declared the spread of Zika in the Americas to be a global emergency in February.

The agency’s statement Saturday made no direct reference to the health experts’ letter, which also highlighted the decades-long collaboration between WHO and the International Olympic Committee. The experts called it an “overly close” relationship that left the U.N. health agency unable to be impartial in Olympic matters.

The IOC rejected the idea that the two organizations were too close, saying it “does not currently have an MoU (memorandum of understanding) with the World Health Organization.” The last one, it added, “outlined cooperation between the two organizations to promote physical activity to fight strokes, heart attacks, diabetes and obesity.”

BEIRUT (AP) – Islamic State militants entered a Syrian opposition stronghold in the country’s north on Saturday, clashing with rebels on the edges of the town as the extremist group built on its most significant advance near the Turkish border in two years, Syrian opposition groups and IS media said.

More than 160,000 civilians are trapped in the fighting, which also forced the evacuation of one of the few remaining hospitals in the area, run by the international medical organization Doctors Without Borders.

On Saturday, IS fighters staged two suicide bombings targeting “opposition forces” near Marea, IS said via its news agency, Aamaq.

Following the suicide bombings, IS militants entered Marea and fighting began inside the town, according to the Syrian Observatory for Human Rights, a Britain-based opposition media outfit that tracks Syria’s civil war.

The territorial gains around the rebel strongholds of Marea and Azaz, north of Aleppo city, are a blow to the Turkey and Saudi-backed rebels, who have been struggling to retain a foothold in the region while being squeezed by opponents from all sides. They also demonstrated the Islamic State group’s ability to stage major offensives and capture new areas, despite a string of recent losses in Syria and Iraq.

The IS offensive targeting Syrian opposition strongholds near the Turkish border began Thursday night.

On Friday, militants of the group captured six villages near Azaz, triggering intense fighting that trapped tens of thousands of civilians unable to flee to safety while Turkey’s border remains closed. A few hundred fled west to the Kurdish-held enclave of Afrin.

People are “terrified for their lives,” the International Rescue Committee said in a statement. The group said it has received confirmed reports that at least four entire families, including women and children, were killed Friday on the outskirts of the town of Azaz.

The IRC runs centers for both children and women in Azaz and provides clean water and sanitation to a camp supporting 8,500 people. More than half the camp’s population has left to find safety elsewhere in the town, it said. The IRC also relocated its staff from the centers and camp to shelter to safer areas of Azaz until the situation enables them to return.

The U.N. refugee agency said it was “deeply concerned” about the fighting affecting thousands of vulnerable civilians.

“Fleeing civilians are being caught in crossfire and are facing challenges to access medical services, food, water and safety,” it said in a statement Saturday.

The advances brought the militants to within few kilometers of the rebel-held town of Azaz and cut off supplies to Marea further south. Marea has long been considered a bastion of moderate Syrian revolutionary forces fighting to topple President Bashar Assad.

Azaz, which hosts tens of thousands of internally displaced people, lies north of Aleppo city, which has been divided between a rebel-held east and government-held west.

A route known as the Azaz corridor links rebel-held eastern Aleppo with Turkey. That has been a lifeline for the rebels since 2012, but a government offensive backed by Russian air power and regional militias earlier this year dislodged rebels from parts of Azaz and severed their corridor between the Turkish border and Aleppo.

The predominantly Kurdish Syrian Democratic Forces (SDF), who are fighting for their autonomy in the multilayered conflict, also gained ground against the rebels.

In recent months, Syrian rebel factions in Azaz – which include mainstream opposition fighters known as the Free Syrian Army along with some ultraconservative Islamic insurgent factions – have been squeezed between IS to the east and predominantly Kurdish forces to the west and south, while Turkey restricts the flow of goods and people through the border.