London crude prices extended gains by more than $1 to near $114 a barrel in electronic trade on Monday, as worries over the worsening situation in Libya fed spreading unrest in the Middle East and stoked fears of a disruption of oil flows in the region.

U.S. crude for April delivery also rose more than $1 above $99 barrel in Globex electronic trading.

Concern about supply disruption from OPEC-member Libya, where revolt against its long-serving president has significantly cut down on exports, on Thursday drove Brent to a 2- year-high of nearly $120 a barrel and U.S. crude to more than $103.

Brent crude for April delivery rose $1.51 to $113.65 a barrel by 2336 GMT, after rising to as high as $113.82 earlier.

U.S. crude for April delivery gained $1.47 to $99.35 a barrel.

Armed rebels who have seized control of Zawiyah, close to the capital Tripoli, were preparing for a counter-attack as Libyan leader Muammar Gaddafi vowed to cling on to his 41-year-old rule.

OPEC and non-OPEC oil producers have plenty of available oil, Qatar Energy Minister Mohammed Saleh al-Sada said on Sunday, adding there was no justification for high levels of nervousness in the market.

In Tunisia, Prime Minister Mohamed Ghannouchi resigned on Sunday after violent protests over his ties to the North African state's toppled former leader, triggering street celebrations in central Tunis.

News that Saudi Arabia had increased its output to more than 9 million barrels per day (bpd) following assurances from Riyadh that it would fill any supply gap helped limit the gains on Friday.

(Reporting by Osamu Tsukimori; Editing by Ed Lane)