The vice-president of the Maldives has been arrested in connection with an alleged plot to assassinate the president, say police and officials.
Ahmed Adeeb was in detention and being charged with high treason, Home Minister Umar Naseer said on Twitter.
President Abdulla Yameen narrowly escaped injury when a blast struck the boat he was using to return home from the airport late last month.
In recent years, the Maldives has been rocked by political infighting.
Mr Yameen's election has been the subject of drawn-out wrangling.
Security has been tightened in the capital Male amid fears of "turmoil" triggered by the arrest, says the Maldivian newspaper Haveeru.
"By early morning Saturday, lorries loaded with policemen and soldiers were seen on nearly every street," it reports.
Three others were also arrested on Saturday - including a former member of Adeeb's security detail and a member of the army's bomb squad, Associated Press news agency reported.
The Maldives Independent website said Mr Adeeb's arrest had "surprised and enthralled many Maldivians".
President Yameen and his wife were travelling to Male from the island where the airport is located on 28 September when their speedboat was hit by the bomb blast.
They had been to the hajj pilgrimage in Saudi Arabia.
The president was unhurt, but his wife and and a number of others were injured when the device went off under a seat normally - but not in this instance - occupied by Mr Yameen.
Soon after the blast, speculation began to grow that Mr Adeeb was involved, reports say. Under the Maldivian constitution, the vice-president succeeds the president if he dies, is incapacitated or resigns.
Officials described the attack as an assassination attempt and had arrested two senior police officers - a week after the president fired his defence minister.
But on Saturday Mr Adeeb too was arrested at the airport as he returned from an official overseas visit "on suspicion of involvement in the boat blast", police spokesman Ismail Ali told AP.
Home Minister Naseer said he was being held on a prison island.
Mr Adeeb, who has denied any links to the explosion, had only been vice-president for three months.
He came to office when the previous vice-president was sacked by Mr Yameen, also on charges of treason.
Who's who in the Maldives
- Abdulla Yameen - became president after 2013 elections that were plagued with problems. He is the half-brother of former President Maumoon Abdul Gayoom
- Mohamed Nasheed - the country's first democratically elected president, he was forced to step down in 2012 in what he described as a coup. Now serving a 13-year sentence under anti-terror laws
- Ahmed Adeeb - vice-president charged with treason in October 2015 in connection with an alleged plot to assassinate President Yameen
- Maumoon Abdul Gayoom - was Asia's longest serving leader until his 30 years of autocratic rule came to an end in 2008
- Mohammed Waheed Hassan - president from February 2012 to November 2013 - he came to power following the disputed resignation of Mohamed Nasheed
- Mohamed Jameel Ahmed - the fourth vice president of the Maldives from 2013 to 2015. Removed from office after he was impeached