Global crude oil prices are not expected to fall in the second half of 2015 and it was still too early to talk about Opec's supply decision when the group meets next in June, Kuwait's Opec governor said on Monday.

"It is expected that there will be some sort of a balance in the oil market in the second half of 2015 which will support prices," Kuwait Opec Governor Nawal Al-Fuzaia told reporters in Kuwait city.

Fuzaia said oversupply in the global oil market is due to slow demand and a rise in production from shale oil, but not from Opec.

Opec production had not increased by more than 200,000 to 400,000 barrels per day above its 30 million bpd cap since 2011.

The Organization of Petroleum Exporting Countries (Opec) said its oil output rose further in April by 18,000 bpd, due to record output in top exporter Saudi Arabia and increases in Iraq and Iran.

Opec ministers next meet on June 5.

Meanwhile, oil prices rose on Monday after Islamic State militants said they had seized control of the key city of Ramadi in western Iraq, raising fears of deeper turmoil in the oil-producing country.

Analysts nevertheless said oil markets remained oversupplied, and that the glut could worsen if US production picked up and output by producer group Opec stayed strong.

Front-month Brent futures were up 37 cents at $67.18 a barrel by 0845 GMT. US crude rose 48 cents to $60.17 a barrel.

Oil services company Baker Hughes on Friday reported US onshore rigs declined for a 23rd week in a row but the rate of that fall has slowed in recent weeks, suggesting the drilling collapse may be coming to an end as prices recover after dropping 60 per cent from June to March. - Reuters