Niamey - An American NGO worker was kidnapped on Friday night in the Niger town of Abalak, northeast of the capital Niamey, before being taken by his abductors to Mali, a security source told AFP."It is too early to determine the identity of the kidnappers, who have returned to Mali. The authorities have put the region on maximum alert", the source said, asking not to be named.Niger's long, porous borders make it occasionally vulnerable to the armed violence that has rocked neighbouring states including Mali in recent years. Northern Mali, which fell under the control of al-Qaeda-linked jihadi groups in 2012 before a French-led military intervention pushed them out, remains subject to attacks by jihadists."At least two people were killed during an exchange of gunfire" as the hostage was being taken, the source said, without revealing the identity of the victims."All roads to Mali are being monitored," the source added.It is the first time that a US national has been kidnapped in Niger.Security problem In January 2011, two young French people were kidnapped from a restaurant in Niamey and were killed shortly afterwards during a rescue attempt.The previous year, five employees of the French energy firm Areva were kidnapped by Al-Qaeda in the Islamic Magreb (Aqim) from a uranium mine in Arlit, north of the country. Four men were freed in 2013 after the earlier release of the sole female hostage.Earlier this month, 22 soldiers from Niger were killed during an attack by armed men who came from Mali to target a refugee camp in the Tahoua region, northeast of Niamey.Three soldiers were also injured, according to Niger's army, which has been deployed along the country's longer border with Mali to prevent armed groups getting in. Niamey is also calling for a diplomatic solution to the conflict in Mali.Despite a peace accord and a 2013 international military intervention, large tracts of Mali are still not controlled by domestic or foreign troops and remain subject to attacks by jihadists."To resolve the security problem in Mali is also to resolve the security problem in Niger", Niger's president Mahamadou Issoufou said during a meeting with German Chancellor Angela Merkel this week.Niger also faces constant attacks in the southeast of the country from Nigerian jihadist group Boko Haram.