Pakistani opposition leader Shahbaz Sharif was arrested on Friday in a longstanding corruption case, the national anti-graft agency said, nine days before crucial by-elections are due to be held.
His brother, ousted prime minister Nawaz Sharif, was sentenced earlier this year to 10 years in prison by the same agency after the Supreme Court removed him from power.
Friday's arrest, by agents of the National Accountability Bureau (NAB) in Lahore, involved a case of alleged corruption in a low-cost housing scheme, called Aashyana (Shelter), when Shahbaz Sharif was chief minister of Punjab province.
"NAB Lahore has arrested former chief minister of Punjab Shahbaz Sharif in Aashyana company case. NAB will produce the former chief minister of Punjab in the honourable accountability court tomorrow," a statement from the agency said.
Information Minister Fawad Chaudhry welcomed the arrest and offered the agency any help it needed.
"This step today is a big step," he told reporters. New Prime Minister Imran Khan's party campaigned on an anti-corruption platform.
Nawaz Sharif has denounced corruption cases against him and his party's leaders as politically motivated, and both brothers deny any wrongdoing. Nawaz Sharif was released from prison last month pending an appeal against his conviction.
The former prime minister was arrested 10 days before the July 25 general election, which was won by Mr Khan, a former cricket star.
The Sharifs' Pakistan Muslim League-Nawaz (PML-N) came in second place in the election. Their party, along with all other major opposition parties, denounced the polls as rigged, accusing the military and courts of tipping the scale in favour of Mr Khan's party.
The PML-N accused the new government of using the anti-corruption agency for political victimisation.
"The government is afraid that the PML-N isn't broken despite all the cheap tactics," party spokeswoman Maryam Aurangzeb said, adding: "It is an attempt to influence the by-election."
By-elections to fill 11 parliamentary seats and 19 provincial assembly seats are scheduled for October 14. Those seats remain empty because of court-ordered delays and the ability of leading candidates to run in several constituencies at once, but only represent one.
The by-elections could affect the slim majority Mr Khan's coalition government holds in parliament, although many of the constituencies are considered strongholds of his Pakistan Tehreek-e-Insaf (PTI) party.
The contests are considered to be closer in the provincial assemblies and could result in the PML-N winning back control of Punjab.