NAIROBI, KENYA - Kenyan riot police fired tear gas Monday to disperse demonstrators gathered in Nairobi for a day of action called by the opposition to protest the country's punishing cost of living crisis, AFP correspondents said.

The government of President William Ruto has vowed to take a tough stance over the demonstrations, which opposition leader Raila Odinga vowed would go ahead despite not receiving police authorization.

Demonstrators also hurled rocks at anti-riot police outside government offices in the capital, while about two dozen people were arrested, including two opposition MPs, correspondents at the scene said.

'We will be here until they run out of tear gas,' said one protester, Markings Nyamweya, 27.

In one part of Nairobi's biggest slum Kibera, demonstrators also set tires alight, AFP journalists said.

'I want Kenyans to come out in large numbers and show the displeasure of what is happening in our country,' Odinga, who narrowly lost last year's election to Ruto, told supporters on Sunday.

Kenyans are suffering from surging prices for basic necessities, as well as a sharp drop in the local shilling against the U.S. dollar and a record drought that has left millions hungry.

'We came here peacefully but they tear gassed us,' said Charles Oduor, 21. 'They lie to us every day. Where is the cheap maize flour they promised? Where are the jobs for the youth they promised? All they do is hire their friends.'

Nairobi police chief Adamson Bungei said Sunday that police received requests to hold two demonstrations only late Saturday and early Sunday, when normally three days' notice is required for public rallies.

'For public safety, neither has been granted,' he said.

'Skyrocketing' cost of living

Interior Minister Kithure Kindiki warned Sunday that anyone inciting public disorder or disturbing the peace would be prosecuted.

'Day of showdown,' was the headline in Kenya's The Standard newspaper on Monday.

Many businesses in Nairobi were shut ahead of the demonstrations, with some employers telling their staff to work from home.

Odinga said he called the demonstrations to protest the 'skyrocketing' cost of living and the 'stolen' election last August.

'Since Mr Ruto was sworn in six months ago, he has continued to run the country with a lot of contempt,' he said, highlighting the high cost of basics such as fuel, cooking oil, school fees and electricity.

Odinga, leader of the Azimio la Umoja party, has long protested that the August election was fraudulent and denounced Ruto's government as 'illegitimate'.

According to official results, Odinga - who was making his fifth bid for the presidency - lost to Ruto by around 233,000 votes, one of the closest margins in the country's history.

The Supreme Court dismissed his appeals, with its judges giving a unanimous ruling in favor of Ruto, finding there was no evidence for Odinga's accusations.

Ruto for his part declared that he would not be intimidated by the opposition demonstrations, saying: 'You are not going to threaten us with ultimatums and chaos and impunity.'

'We will not allow that,' he said, calling on Odinga to act in a 'legal and constitutional manner'.