West Africa's regional body, Ecowas, has urged Liberians to stay calm after the suspension of the speaker of parliament on corruption allegations.
Dweh denies the corruption allegations
Ecowas said it was deeply concerned by heightened tensions and would send a team to investigate the claims.
The suspended speaker, George Dweh, is a founder of the Lurd former rebels and the UN says some militia leaders have threatened to return to war.
UN police guarded parliament as George Kaukau was voted in as the new speaker.
Mr Kaukau is a loyalist of former President Charles Taylor.
Mr Dweh was named speaker under a 2003 deal to end 14 years of war.
Mr Dweh denies accusations that he and three colleagues had embezzled $92,000.
He had threatened to go to work on Wednesday in defiance of his suspension but he remained in his residence.
Ecowas said its investigators would arrive on Friday and said anyone found guilty would be sanctioned "without fear or favour."
UN troops are disarming former fighters
The head of Unmil, the UN mission in Liberia, Jacques Klein, said he had learnt of a letter sent by "generals" to international mediators, in which they threatened to once more take up arms.
"Unmil strongly warns that it will deal firmly and decisively with any attempt to derail the peace process," he said.
The increased tensions come even though the suspended officials come from all of the different armed factions, which formed a power-sharing government to end the war.
Mr Dweh's deputy Edditon Varmah was an ally of former President Charles Taylor.
One of the two other suspended MPs is from another former rebel group, Model, and the second was nominated by civil society.
The four were suspended and their pay withheld until the money was repaid.
Elections for Liberia's first post-war government are due on 11 October.