REUTERS - An international coalition is pushing back Islamic State militants in their Syrian and Iraqi strongholds, but the group is threatening Libya and could seize the nation's oil wealth, U.S Secretary of State John Kerry said on Tuesday.

Officials from 23 countries met in Rome to review the fight against Islamic State militants, who have created a self-proclaimed Caliphate across swathes of Syria and Iraq, and are spreading into other countries, notably Libya.

While Western officials worry about the growing threat posed by Islamic State in the former Italian colony, there was no suggestion that foreign powers were preparing to launch a major military offensive against them there for now.

Islamic State forces have attacked Libya's oil infrastructure and established a foothold in the city of Sirte, exploiting a power vacuum in the North African country where two rival governments have been battling for supremacy.

"That country has resources. The last thing in the world you want is a false caliphate with access to billions of dollars of oil revenue," Kerry said.

Under a U.N.-backed plan for a political transition, Libya's two warring administrations are expected to form a unity government, but a month after the deal was agreed in Morocco, its implementation has been dogged by in-fighting.

Kerry said the two sides were "on the brink of getting a government of national unity". Italian Foreign Minister Paolo Gentiloni said once it was in place, many countries would be prepared to respond to any request for help with security.

However, Kerry said the United States was opposed to deploying any of its ground forces into Libya and French Foreign Minister Laurent Fabius dismissed media speculation that Paris was poised to intervene in the oil-rich country.

"That is totally inexact," he told reporters in Rome.

The United States is leading two different coalitions carrying out air strikes in Iraq and Syria that have targeted Islamic State, but the jihadist group has been left largely left untouched in Libya.

"We are still not at the victory that we want to achieve, and will achieve, in either Syria or Iraq and we have seen Daesh playing a game of metastasizing out to other countries, particularly Libya," Kerry said, using a pejorative Arabic term for Islamic State.

INTERRUPTING ISLAMIC STATE

Defense ministers from the anti-IS group are due to meet in Brussels next week to discuss further options, while Kerry said he expected further consultations with allies at a security conference in Munich, Germany later this month.

While the Islamic State remained undefeated, it had suffered many setbacks, Kerry said, losing 40 percent of the territory it once controlled in Iraq and 20 percent of its lands in Iraq.

"Our advances .. are undeniable. We have launched nearly 10,000 air strikes, we have interrupted their finance mechanisms, they have had to cut the salaries of their fighters, we have interrupted their capacity to get revenues," Kerry said.

The one-day Rome meeting took place as talks have begun in Geneva to try to end the five-year-old Syrian civil war, which has killed at least 250,000 people, driven more than 10 million from their homes and drawn in the United States and Russia on opposite sides.

While Washington has long said Syrian President Bashar al-Assad has lost the legitimacy to lead, it has made clear that its first priority is to try to rein in Islamic State group.

"If you want to beat Daesh quickly, then get a negotiated deal to end the Syria war," Kerry said.

Tuesday's meeting also covered stabilizing areas such as the Iraqi city of Tikrit, which has been wrested from the group, as well as broader efforts to undercut its finances, stem the flow of foreign fighters and counter its messaging, officials said.