The leaders of the G7 group have said the world economy is an urgent priority and cautioned that a British vote to leave the European Union would seriously threaten global growth.

In a statement following a two-day summit in the Japanese resort of Ise-Shima, the world's seven leading industrial nations pledged to "collectively tackle" major risks to global growth and committed to a cooperative approach in beefing up policies to stimulate their sluggish economies.

"Global growth remains moderate and below potential, while risks of weak growth persist," the G7 leaders said in a declaration on Friday.

"Taking into account country-specific circumstances, we commit to strengthening our economic policy responses in a cooperative manner and to employing a more forceful and balanced policy mix, in order to swiftly achieve a strong, sustainable and balanced growth pattern," the G7 statement said.

'Serious risk'

Last month, the International Monetary Fund cut its global economic growth outlook for this year to 3.2 percent, compared with a forecast of 3.4 percent in January.

For 2017, the IMF said the global economy would grow 3.5 percent, down 0.1 percentage point from its January projection.

The G7- made up of Britain, Germany, Canada, France, Italy, Japan and the United States - also warned that a British secession from the EU in next month's referendum could have disastrous economic consequences.

WATCH: Inside Story - How would a Brexit affect global power balance?

"A UK exit from the EU would reverse the trend towards greater global trade and investment, and the jobs they create, and is a further serious risk to growth," they said.

The comments highlight international concern over the possibility of so-called Brexit, as UK voters prepare for a June 23 referendum to decide whether to leave the 28-country bloc.

"This summit is sending the signal that all of us hope that Great Britain remains a member of the European Union," German Chancellor Angela Merkel said.

"But of course the decision has to be made by the British voters."

Gap widening

David Cameron, the UK prime minister, has been campaigning for Britain to stay in, with recent polls suggesting a widening lead for supporters of continued EU membership.

However, the "leave" campaign is putting up stiff competition, with a number of prominent supporters, including former London mayor Boris Johnson.

Al Jazeera's Scott Heidler, reporting from Tokyo, said "Brexit" was not a primary issue in the G7 summit.

However, leaders wanted it to be identified in the statement published after the summit and it was included in the document, he said.

"There was obviously no back-and-forth discussion on this issue," he said.

Separately, the G7 called large-scale immigration and migration a major challenge.

It pledged to increase global aid for the immediate and long-term needs of refugees and displaced people.

"The G7 recognises the ongoing large-scale movements of migrants and refugees as a global challenge which requires a global response," the leaders said.

INTERACTIVES: Islands row around China

They said they would "commit to increase global assistance to meet immediate and longer-term needs of refugees ... as well as their host communities".

The group also expressed concern over the East and South China Seas, where China has been taking more assertive action amid territorial disputes with Japan and several Southeast Asian nations.

Without mentioning China, which has claims to almost the entire South China Sea, the G7 reiterated its commitment to the peaceful settlement of maritime disputes and to respecting the freedom of navigation and overflight.