Pakistan began quarantining at least 200 people near the Iranian border, officials said Monday, as fears spiralled over the growing toll from the coronavirus in the region amid allegations of a coverup in Iran.

The quarantine announcement came hours after Pakistan sealed off its land border with Iran while neighbouring Afghanistan said it had detected its first infection. 

It also came as Iranian authorities denied allegations of an official coverup following reports that dozens of deaths had gone unreported in the country.

In Pakistan's southwestern Balochistan province authorities moved fast to quarantine at least 200 people after Shiite Muslim piligrims returning from Iran entered the country and briefly interacted with other residents.

"We have decided not to take a chance and keep all of them under observation for the next 15 days," Najeebullah Qambrani, assistant commissioner at the Taftan border crossing, told AFP, saying 250 people were being quarantined.

Balochistan's secretary of health Mudassir Malik confirmed the quarantine but estimated that between 200 and 250 were being held.

He added that around 7,000 pilgrims had returned to Pakistan from Iran this month alone.

Afghanistan and Pakistan share long, porous borders with Iran that are often used by smugglers and human traffickers, while millions of Afghan refugees currently live in the Islamic Republic -- raising fears that the virus could easily spread over the border.

Pakistan -- bordered by China to the north and Iran to the south -- also suffers the additional burden of having a lacklustre healthcare system following decades of under-investment by the state, leaving impoverished, rural communities especially vulnerable.

Balochistan in particular is woefully unprepared to handle a public health emergency after being beset for decades by a separatist insurgency, jihadist violence, and neglect from the central government.

The novel coronavirus has spread to more than 25 countries, with more than 2,500 dead in China, and is causing mounting alarm due to new pockets of outbreaks in Europe, the Middle East and Asia.