Kenyan troops have pushed further into southern Somalia, after crossing the border to fight the militant group al-Shabab.

Residents of the area said Monday that Kenyan troops, backed by armored vehicles, were near the village of Qoqani, which al-Shabab abandoned on Saturday.

Al-Shabab has vowed to fight back against the Kenyans, calling on all Somalis to defend against “the enemy.” There are reports that the militants have seized and assembled a large number of trucks in the Lower Shabelle region, near the capital, Mogadishu.

Kenyan authorities blame al-Shabab for a series of recent kidnappings that could jeopardize Kenya's status as a safe tourist destination.

The kidnapping victims include a British tourist, a French woman and two Spanish aid workers. The Spaniards, with the medical aid group Doctors Without Borders, were kidnapped Thursday from Kenya's massive Dadaab camp for Somali refugees.

Kenyan forces have crossed into Somalia before, although this incursion appears to be on a larger scale.

Saturday, Internal Security Minister George Saitoti announced Kenya would fight back against al-Shabab, “wherever they will be.” Al-Shabab controls large sections of southern Somalia, including some areas near the border.

A Kenyan military helicopter crashed on the Kenyan side of the border late Sunday, killing five Kenyan military personnel. Kenyan defense officials confirmed it was part of the contingent sent to fight al-Shabab but said the crash was caused either by pilot error or a mechanical malfunction.