SANAA, Yemen (AP) — Deaths resulting from a diphtheria outbreak in Yemen are "likely to rise" if the naval blockade imposed by a Saudi-led coalition fighting to defeat Shiite rebels in war-torn Yemen remains in place, an international aid group warned on Monday.

Save the Children said in a statement that Yemeni children are bearing the brunt of what it described as a "the worst diphtheria outbreak for a generation." It also said that its aid workers have been struggling to cope with the disease which has killed at least 52 people, mostly among children under 15, and is believed to have infected some 716 others since August. Diphtheria is a contagious and potentially fatal disease that primarily infects the throat and airways.

There's so little help right now that families are carrying their children for hundreds of miles to get to us," Mariam Aldogani, the group's field coordinator in Hodeida, said. "But they're arriving too late and infecting people on the way."

The outbreak has hit Ibb and Hodeida provinces the hardest, the aid group said.

Yemen has been embroiled in a civil war since March 2015, pitting Iran-backed Shiite rebels, known as Houthis, against the coalition backing the internationally recognized government of Abed Rabbo Mansour Hadi. The near three-year stalemated war in Yemen has damaged its infrastructure, crippled the health system and pushed the Arab world's poorest country to the brink of famine.

The U.N. has called Yemen the world's worst humanitarian crisis with more than 22 million people in need.

Save the Children said that aid efforts have been largely hampered due to the blockade on the key Red Sea port of Hodeida, a lifeline for most of Yemen's population as it handles about 70 percent of the country's imports. The Saudi-led coalition has imposed a blockade on Yemen since the beginning of the war but has recently eased it on ports allowing access for commercial vessels.

The aid group said the partial easing of the blockade is still far from enough to meet the Yemenis' dire humanitarian needs. "Any tightening of the blockade could have a devastating impact on children," it added.

The impoverished country is already grappling with a cholera epidemic since October 2016. The outbreak, which escalated in April, killed some 2,000 people and infected over a million others