"closer cooperation" is a perfectly acceptable phrase in written English.
For example, "The two countries agreed to move forward with closer cooperation in the areas of trade and foreign policy."
Nevertheless, the current trend is toward closer cooperation.
Kaplan holds open the possibility that nascent great-power rivalry will lead to ever closer cooperation.
We'll intensify our efforts to encourage closer cooperation between Pakistan and Afghanistan.
The territorial churches in Germany had sought closer cooperation among themselves for many years.
Ri's trip to Russia could herald closer cooperation with North Korea.
In the short term, I think we will see more of this kind of closer cooperation".
We need closer cooperation between Iraqi and coalition forces, as in CAP.
To make further advances, Dr. Pew said, will require closer cooperation between psychologists and computer scientists.
That is intended to foster closer cooperation between the sales and promotion functions.
"Only with closer cooperation and mutual help can we overcome the crisis," he said.
They called for closer cooperation in preventing terrorists from moving money around the world.
