SINGAPORE » Singapore and Malaysia urged Indonesia on Friday to stop illegal fires whose smoke has drifted across the southern Malay peninsula and worsened air pollution in the region in recent days.

Singapore Foreign Minister George Yeo told his Indonesian counterpart Marty Natalegawa in a telephone conversation Friday that smoke from neighboring Sumatra island has significantly increased cases of respiratory problems such as asthma, the foreign ministry said in a statement.

Natalegawa assured Yeo that Indonesia would address the haze problem, the ministry said.

Indonesian farmers periodically set fires to clear land and the smoke often drifts about 50 miles (80 kilometers) across the Straits of Malacca to Singapore and southern Malaysia. Singapore’s air pollution index rose Thursday to the unhealthy level for the first time since 2006.

Air conditions improved slightly Friday with the air index hovering just below the unhealthy level.

"It’s a matter of very serious concern as a health hazard that has not just affected Singapore but also the southern part of Western Malaysia," the ministry said.

Soccer officials postponed two Singapore League games late Thursday and Malaysia shut down more than 200 schools in the southern town of Muar because of the haze on Thursday. Schools reopened Friday as air quality improved slightly, but officials distributed face masks and bottled water to students.

"We want action before the haze spreads and becomes more detrimental in Malaysia," Malaysian Deputy Prime Minister Muhyiddin Yassin said late Thursday, according to the Bernama news agency.

Doctors are recommending residents limit outdoor exercise while some Singaporeans are donning face masks to keep out the smoky air. Singapore, which normally has bright sunshine or rain, has been coated in a smelly smoke fog since Wednesday.

"It’s pretty bad this time," said Myra Abdullah, a 21-year-old office worker. "I’ve had a sore throat for a couple days. Indonesia is not being a good neighbor at all."