Gunmen have kidnapped five oil workers of Nigerian energy firm Sahara Energy Oil Company in the southern oil-rich Delta state, hours after the most notorious militant group had warned of imminent attacks on Nigeria’s oil infrastructure, local media report.

Suspected gunmen abducted the workers on Wednesday on the border between the states of Edo and Delta, Vanguard newspaper quoted Delta State police spokesperson Andrew Aniamaka as saying.

Last week, the Niger Delta Avengers (NDA)—the militant group responsible for most of the 2016 attacks on Nigeria’s oil infrastructure threatened to unleash the deadliest round of attacks on Nigeria’s oil sector—“in a few days time”.

The kidnapped oil workers were traveling in a boat en route to an offshore location when the gunmen arrived, local resident Ajugu Fidelis, who witnessed the abductions, told Vanguard.

“The police in partnership with the military are working to ensure that the victims are rescued unhurt with the perpetrators arrested and brought to book,” Delta State police’s spokesman Aniamaka said.

The reports of the oil workers’ abduction came just as a Nigerian police spokesman said on Saturday that two Americans and two Canadians who had been abducted in a northern Nigerian state were freed.