By Jennifer Rigby and Christy Santhosh

(Reuters) - More children were left out of critical vaccination drives for diseases such as diphtheria, tetanus and whooping cough last year as a rise in conflicts across the globe hindered the supply of life-saving shots mostly in strife-torn regions, the United Nations said on Monday.

About 14.5 million children failed to get vaccinated in 2023, compared with 13.9 million a year earlier, according to U.N. estimates. The number, however, was lower than during the COVID-19 pandemic, when about 18 million children missed out on vaccination.

The U.N. also said that an additional 6.5 million children failed to receive more than a single dose, meaning they were not fully protected.

The estimates are based on how many children received either the first dose or all three doses of the DTP vaccine, a staple shot that protects against diphtheria, tetanus and pertussis, also known as whooping cough.

In total, 84% of infants globally received their full course last year, below the necessary level to prevent disease outbreaks.

War-hit countries in particular saw a big jump in the number of children who were not immunized in 2023, the United Nations Children's Fund (UNICEF) and the World Health Organization (WHO) said at a press conference last week, ahead of releasing the data.

The biggest fall in vaccination coverage globally was in Sudan, which has been decimated by 15 months of civil war. It saw coverage rates fall to 57% in 2023 from 75% in 2022.

That meant nearly 701,000 children in Sudan were not vaccinated at all against killer diseases such as measles and diphtheria.

The number of children who failed to get immunized in the occupied Palestinian territories rose to 17,000 for the nine months last year based on data available until September from 1,000 in 2021, the agencies said.

Sudan, Yemen and Afghanistan were all new entrants on the list of the 20 countries with the most unvaccinated, or "zero-dose," children in 2023.

More than half of the world's unvaccinated children live in countries with fragile, conflict-affected or vulnerable settings, although these nations only make up 28% of the global birth cohort, the UNICEF said.

There were some positives in the U.N. report. For example, there were around 600,000 fewer "zero dose" children across the African region in 2023 than in 2022, and coverage of the HPV vaccine, which protects against cervical cancer, also improved globally. Ukraine also saw an improvement despite its war with Russia.

(Reporting by Jennifer Rigby and Christy Santhosh; Editing by Anil D'Silva)