The move comes after President Kumaratunga sacked three senior ministers and suspended parliament for two weeks on Tuesday.
Amid political uproar, the president has said she is ready to open peace talks with Tamil rebels after sacking key ministers in her cabinet.
In a televised national address on Tuesday, Kumaratunga said she would enter into negotiations with the Liberation Tigers of Tamil Eelam (LTTE) despite rejecting their blueprint for peace earlier in the day.
"I remain willing to discuss with the LTTE a just and balanced solution of the national problem, within the parameters of the unity, territorial integrity and sovereignty of Sri Lanka," she said.
She made no reference to the LTTE's own political plan, unveiled on Saturday and rejected by her Sri Lanka Freedom Party (SLFP) as being a stepping stone to partition.
But she accused the government of Prime Minister Ranil Wickremesinghe of making too many concessions to the rebels in recent peace negotiations.
The speech came after Kumaratunga sacked the ministers of defence, interior and information and suspended parliament for 15 days.
"I appeal to all my fellow citizens to remain calm... I will not tolerate revenge and lawlessness from whatever quarter it may come," she said.
"The maintenance of law and order is one of the paramount duties cast on me under the constitution. It is a duty I will discharge with the co-operation of the security forces and all the people of Sri Lanka."
Prime Minister Wickremesinghe
is visiting the US
Kumaratunga is in an uneasy coalition government since her party lost parliamentary elections in December 2001 to Prime Minister Ranil Wickremesinghe's United National Party.
Her actions come as her arch-rival Wickremesinghe was set to hold talks with US President George Bush at the White House on Wednesday.
Wickremesinghe has already condemned Kumaratunga for "trying to plunge the country into chaos and anarchy".
The European Union has also expressed concern at the political turmoil in Sri Lanka.
The EU said the political coexistence between the rival parties of Kumaratunga and Wickremesinghe had "contributed significantly" to progress made in peace talks with the LTTE.
But Tuesday's events "may put at risk the spirit of coalition which has proven vital for the sustained forward momentum of the peace process", the 15-nation EU said in a statement with the Executive Commission.
The Italian presidency and commission "urge the two principal parties to continue to work together in support of a negotiated political solution, as envisaged by the peace process," the statement said.
"The goals of peace and prosperity that Sri Lanka so much
deserves can only be achieved through the continued cooperation and commitment by all the players involved."
Sri Lanka has been plagued by civil war for more than two decades.
Minority Tamils are fighting for autonomy in the country's north and east, while majority Sinhalese are divided on whether to give it to them.
The war has cost the Indian Ocean island more than 60,000 lives.