Interior Minister Selami Altinok said the deputies from the Peoples' Democratic Party (HDP) would not be allowed into Cizre for their own security.

The government says it has launched a military operation in Cizre, a city of 120,000 close to the borders with Syria and Iraq, and imposed a curfew to eliminate Kurdistan Workers Party (PKK) militants after a string of attacks inside Turkey.

The HDP however says that 21 civilians, including children, have been killed in the operation and a humanitarian crisis is worsening by the day.

HDP co-chairman Selahattin Demirtas has been leading fellow deputies and dozens of supporters on a march to Cizre to end the curfew and draw attention to the plight of its residents.

Also part of the group are Turkey's EU Affairs Minister Ali Haydar Konca and Development Minister Muslum Dogan -- HDP MPs who joined the caretaker government ahead of snap elections due on November 1.

But security forces in full riot gear and brandishing shields Thursday stopped them outside Idil, a town several dozen kilometres (miles) west of Cizre, an AFP correspondent said.

"We will not allow them to go to Cizre," Altinok told reporters in Ankara. "It is our duty to protect them."

Anltinok said 30-32 members of the PKK had been killed by the armed forces in the Cizre military operation.

He said that 800 kilogrammes (1,760 pounds) of explosives had been destroyed, 10 suspected PKK members arrested and caches of arms seized.

He added that one civilian had been killed in clashes.

Altinok said that the curfew, which is now in its seventh day, would continue for as long as necessary and insisted it was in line with the law.

"As soon as our activities (the military operation) are completed, we intend to lift the curfew."

- 'State holding people hostage' -

Pro-Kurdish media quoted HDP Mardin deputy Mehmet Ali Aslan, who is currently trapped in Cizre, as saying at least eight civilians were killed in attacks by Turkish forces overnight.

"It is impossible to go out and buy bread, the water supply is failing and there is no electricity," the HDP quoted Demirtas as saying Thursday on the road to the city.

"In Cizre, 120,000 people have been held hostage by the state for a week," he added.

He said that the corpses of young girls and boys caught in the crossfire could not even be buried.

"They put ice on the corpses to stop them putrefying. Because burials are banned."

Demirtas described Cizre as "Turkey's Kobane" referring to the Syrian Kurdish town that was the subject of a hugely symbolic battle between Kurds and jihadists up to January this year.

He added that Cizre was being punished for voting "94 percent for the HDP" in June 7 elections where the ruling party of President Recep Tayyip Erdogan lost its overall majority.

Tensions have soared in Turkey in recent days after the PKK killed dozens of members of the Turkish security forces in attacks and nationalists raided HDP offices across the country.

Stepping up the pressure on Demirtas, prosecutors in the southeastern city of Diyarbakir late Wednesday opened an investigation against the HDP leader for "insulting the nation" and "making propaganda for a terror group" over comments made at a news conference earlier that day.

If he is charged and a trial goes ahead, Demirtas could face up to 19 years in jail, the official Anatolia news agency said.

Meanwhile prominent HDP MP and Sakharov Prize laureate Leyla Zana, who was jailed from 1994-2004 over alleged links to the HDP, said she was prepared to go on a hunger strike "to death" if the violence did not stop.