Turkey's Deputy Prime Minister, Husametin Ozkan, and two other ministers have resigned from the country's beleaguered coalition government.

The three men are also reported to have left Prime Minister Bulent Ecevit's Democratic Left party, depriving it of its position as the largest coalition partner in the government.

The BBC's correspondent in Istanbul, Jonny Dymond, says there is now enormous pressure on Mr Ecevit himself to resign, and early elections seem unavoidable.

Turkey needs new political formations to open the way of politics, which is now deadlocked and passive

Istemihan Talay, resigned culture minister

The prime minister's poor health has kept him away from office since early May and he has already rejected numerous calls to step down.

The turmoil has been accompanied by fresh trouble for the Turkish economy, with the value of its currency plunging by nearly 5% on Monday.

The United States is said to be monitoring the situation "with interest".

As the only Muslim-majority member of Nato, Turkey's political and economic stability are important to a variety of US interests abroad - including the Middle East, Afghanistan and Iraq.

Loss of 'key ally'

Our correspondent says the catalyst for the ministers' resignations seems to have been a call on Sunday for early elections from the leader of the Nationalist Action Party (MHP), now the largest coalition partner.

The tension was heightened at the weekend when Mr Ecevit publicly attacked his deputy for failing to back him in the wake of mounting criticism.

Prime Minister Bulent Ecevit saw Mr Ozkan as a key ally

Correspondents say Mr Ozkan - who always preferred to keep a low profile - had been the prime minister's key ally and possible successor.

He reportedly acted as a mediator, resolving disputes over economic reforms with other parties.

As well as the deputy prime minister, Culture Minister Istemihan Talay and State Minister Recep Onal - both of whom belonged to Mr Ecevit's DSP - resigned.

Mr Talay told local media that the number of resignations "could increase".

"Turkey needs new political formations... to open the way of politics, which is now deadlocked and passive," he said.

Market tumble

The market has taken the political crisis hard, with the currency and share prices plummeting.

The Turkish lira hit an all time low against the dollar, losing 20% of its value. Interest rates have jumped by 15%.

Markets are worried that a new government will not stick to the programme hammered out with the International Monetary Fund in return for a $16bn loan agreed earlier this year.

Ministers were also in a rush to pass reforms necessary so that membership negotiations with the EU might start. The end of the year is the effective deadline.

With early elections looking like a necessity, there will be no legislative progress for months, which is likely to unsettle the business community still further.