SINGAPORE - Singapore Prime Minister Lee Hsien Loong said that it was gracious of Indonesian President Susilo Bambang Yudhoyono to apologize to Singapore and Malaysia for the transboundary haze resulting from forest burning in Sumatra, Indonesia, local media reported on Wednesday.

"We accept his apology wholeheartedly. I welcome President Yudhoyono's promise to spare no efforts to tackle this serious problem which has caused suffering to the people of Singapore, Malaysia and Indonesia," the Prime Minister's Office quoted Lee as saying in a statement.

The severe haze has been troubling Singapore and Indonesia as the wind drives the smog over the two countries in the dry monsoon season, which typically lasts from June to October.

Singapore continued to be affected by a smog despite a thunderstorm on Tuesday, though it is less severe than previous days when the pollutant standards index shot up to the unprecedented level of over 300, indicating that the air quality was "hazardous".

There is still the traditional way of clearing land for farming purposes with fire in some parts of Indonesia, despite the law prohibiting such practices. Some of the palm oil plantations are reportedly involved, too.

It leads to a haze in neighboring countries almost each year.

The Indonesian president has said that the police would investigate the man-made causes of the fires and take the necessary legal action against those responsible.

"I hope that Indonesia will also take swift and sustained action to put out the forest fires and stop the illegal land clearing practices," Lee said in the statement.

He also reiterated Singapore's offer of assistance to Indonesia in putting out the fires, saying that Singapore stands ready to work closely with Indonesia, Malaysia and others in the region to bring the haze-related problems to an end.

"We need to put in place a permanent solution to prevent this problem from recurring annually," he said.