Thai Prime Minister Somchai Wongsawat Thai has rejected calls for new elections, in a major escalation of tensions with protestors who have seized the country's main airport.
He earlier arrived back in the northern city of Chiang Mai.
Thailand's powerful army chief, General Anupong Paojinda, had urged Mr Somchai to call new elections, but anti-government protestors said new elections would not solve the political crisis.
They also refused to end their occupation of Bangkok's international airport.
Leading activist Pibhop Dhongchai said that if Mr Somchai resigned, they would talk again about whether they would negotiate.
Anti-government protestors have occupied the control tower at Bangkok's main international airport since yesterday. They stormed the main terminal, forcing airlines to cancel flights.
The People's Alliance for Democracy later agreed to allow the Thai airports authority to evacuate 3,000 stranded passengers, although the airport is expected to remain closed for the rest of the day.
The leader of a pro-government group has urged supporters to march in Bangkok, raising the prospect of street clashes with anti-government protestors.
The Department of Foreign Affairs has issued a warning to any Irish citizens planning to travel to the area.
They are advised to exercise extreme caution as the situation remains highly volatile and unpredictable.
Police have reported a series of small bomb blasts at the airport, injuring several anti-government protestors.
One bomb wounded four members of the People's Alliance for Democracy, hours after the PAD stormed the airport in a dramatic escalation of its six-month campaign to oust Mr Somchai.
The Nation newspaper said on its website three explosions had been heard outside the $4bn Suvarnabhumi airport terminal, the gateway for nearly 15m tourists to Thailand last year.
A fourth blast appeared to target PAD supporters in another part of Bangkok.
12 people were wounded in the overnight attacks, but police have not confirmed the casualties.
Meanwhile, Thailand's finance minister has expressed fears that the protests could have a damaging effect on the economy, which depends on tourism.
