DHAKA (AFP) -- Bangladesh's government Saturday postponed handing over power to a caretaker administration amid violent clashes between supporters of the outgoing government and opposition, officials said.

More than 15,000 police were deployed on the streets of the capital Saturday as the government's mandate expired and street clashes over two days killed at least four people and left dozens injured.

Officials said former Supreme Court justice K. M. Hasan who is due to take over as head of the caretaker body was sick and therefore no date had yet been fixed for him to be sworn in.

"The date and the timing of the swearing in will be announced later. But it will take time," presidential spokesman Mukhlesur Rahman Chowdhury told AFP.

The government has up to 15 days from midnight Friday to hold the ceremony although it said earlier this week it would probably take place on Friday or Saturday.

The announcement came as supporters of the opposition Awami League and outgoing Bangladesh Nationalist Party (BNP) fought with guns, bombs and sticks as the mandate of Prime Minister Khaleda Zia's coalition government ended. The Awami League accuses Hasan, a former BNP official, of being partisan and has vowed to bring the country to a standstill when he is sworn in to oversee polls which are due to be held within 90 days

The outgoing premier appealed for calm in a televised speech late Friday.

"As our tenure is over, we want peace to continue in the country, especially before the next general election. Keep peace in the country. Let peace continue," she said.

Police banned all public gatherings at the main square in Dhaka from midnight Friday in an attempt to avert further clashes.

The Awami League party says it cannot accept Hasan as the head of the supposedly impartial body which is meant to ensure that a ruling party cannot rig polls.

Talks between the two parties on the issue broke down earlier this week with both sides refusing to give any ground.

In addition to objecting to the government's decision to appoint Hasan as head of the caretaker government, the Awami League and its 13 leftist allies also want the head of the Election Commission M.A. Aziz and his two deputies replaced.

It says the commission has drawn up a voters' list that includes millions of ghost voters and leaves out many opposition members.

Zia's BNP has led a four-party Islamist-allied coalition since ousting the Awami League at the last polls in October 2001.

In another development, 13 key BNP politicians, including two ministers, defected to a new Liberal Democratic Party Thursday, accusing their old party of fostering the rise of Islamic fundamentalism in the mainly Muslim country of 144 million.

The new group said it wanted to bring an end to the BNP and Awami League's monopoly on power. The two parties have alternated in government since 1990.

It also accused the BNP of turning a blind eye to the militants' activities because of the two Islamic parties in its coalition.

"The present BNP is a corrupt party that has cheated the whole country and moved away from the goal its founders set by becoming an Islamic fundamentalist party," the new party's joint secretary general, Firoz M. Hasan, told AFP.

Zia admitted last year her administration had underestimated the danger posed by religious extremists who carried out a string of deadly attacks killing at least 28 people.

The bombings, which included the country's first suicide attacks, were blamed on the banned Jamayetul Mujahideen Bangladesh and its campaign to impose Islamic law in the secular country. Its top leaders have been sentenced to death.