Israel flooded the occupied West Bank with reinforcements on Wednesday in the hunt for six Palestinians who have been on the run for three days after escaping from a maximum-security prison.
The army said that in the search for the men, "it has been decided to extend the general closure" of the West Bank.
It said the closure would last until midnight on Friday, "subject to a situational assessment".
Commander Aviv Kohavi decided to reinforce Israeli Defence Force troops "with combat battalions, observation troops and a number of IDF aircraft that are observing the area to assist in capturing the security prisoners and thwart terrorist attacks in the region", the army said.
Demonstrations were held in support of the fugitives, who broke out of Gilboa prison in northern Israel, in several West Bank towns late on Wednesday, including Ramallah and East Jerusalem, AFP reported.
In Nablus, youths set tyres alight during confrontations with Israeli security troops. The Palestinian Red Crescent said 60 protesters were injured by tear gas near Nablus.
Of the six escapees, five are members of the Islamic Jihad militant group and one is from Fatah, the faction of Palestinian President Mahmoud Abbas.
They staged their jailbreak on Monday through a hole they had dug under a sink in a prison cell, reportedly using a spoon.
Earlier, the Palestinian Prisoners' Club said Israeli troops had arrested at least six relatives of the men.
Israel has used drones, set up road checkpoints and sent an army mission to Jenin, the flashpoint West Bank home town of many of the men locked up for their roles in attacks on Israelis.
The Palestinian Prisoners' Club said two brothers of Mahmud Ardah, described in local media as the mastermind of the breakout, were arrested.
It said four other people – Dr Nidal Ardah, two brothers of Mahmud's cousin and fellow fugitive Mohammad Ardah, and the father of escapee Munadel Infeiat – were also taken into custody.
Amani Sarahneh, a spokeswoman for the prisoners' group, said that others could also have been arrested, and that some were only briefly detained.
The Israeli army, which has occupied the West Bank since 1967, confirmed that "several arrests were made overnight", without elaborating.
"Holding someone in order to coerce a relative to do something is a mafia-style tactic," tweeted Omar Shakir, Israel and Palestine director for Human Rights Watch.
An Israeli injunction is in effect against publishing details of the jailbreak investigation, even as local media report on the rush to recover from the embarrassing lapse and prevent any possible attack by the fugitives.
Those on the run include Zakaria Zubeidi, a former militant leader from Jenin.
Gilboa prison, which opened in 2004 during the second Palestinian Intifada, or uprising, is a high-security site where hundreds of Palestinians are detained among other inmates.
The prison service said all of those held at Gilboa for "security offences" were being relocated in case more tunnels were dug.
The prisoners' group reported "tension" in jails on Wednesday, and a spokeswoman for the Israeli prison authorities said fires had been lit in Ktziot and Ramon jails.
"The situation is now under control. The fires have been extinguished," the spokeswoman said.
When news of the escape first broke on Monday, many people in the Gaza Strip and in Jenin took to the streets to celebrate.