By Syed Raza Hassan

KARACHI, Pakistan (Reuters) - Pakistan's southern province of Sindh extended the closure of all educational institutions following the confirmation of a second coronavirus case in Karachi, the country's largest city.

Pakistan has confirmed four cases of coronavirus, three of them involving people who had traveled to neighboring Iran, one of the countries hardest hit by the outbreak that began in China in December.

While two of the confirmed cased were in the southern port city of Karachi, the other two were in the capital Islamabad.

Schools in Sindh have been closed since Thursday, after the first case in Karachi was confirmed.

"The Sindh government has decided to keep the schools closed till March 13, so the isolation period of the suspect cases could be completed," Saeed Ghani, provincial education minister told Reuters on Monday. "We don't want to take any risk."

Schools in Islamabad have remained open, but the thinly populated western province of Baluchistan, which borders Iran, closed its schools last week.

Pakistan suspended all flights with Iran and closed the land border last week.

Health Minister Zafar Mirza has said that government is gradually allowing pilgrims to return from Iran, after holding them in quarantine at the border for 14 days.

Around 700 pilgrims arrived in Karachi from Iran over the weekend, the Sindh chief minister's office said in a statement.

(Additional reporting by Gul Yousafzai in Quetta; Editing by Simon Cameron-Moore)